[stdlib] Remove unnecessary doc comments from hashValue implementations

When implementing a protocol requirement, additional doc comments are
unnecessary unless there are additional semantics peculiar to the specific
implementation.

The manually propagated documentation had several problems, including copypasta
and inconsistent terminology.

Therefore, if `T.==` doesn't have any doc comments and the implementation of
`T.hashValue` is unremarkable, remove the unnecessary doc comment.

Author: xwu

stdlib/public/core/Arrays.swift.gyb

@@ -2298,13 +2298,7 @@ extension ${Self} : Equatable where Element : Equatable {
 }
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
-extension ${Self}: Hashable where Element : Hashable {
-  /// The hash value for the array.
-  ///
-  /// Two arrays that are equal will always have equal hash values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
+extension ${Self} : Hashable where Element : Hashable {
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {

stdlib/public/core/ClosedRange.swift

@@ -386,12 +386,6 @@ extension ClosedRange: Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension ClosedRange : Hashable where Bound : Hashable {
-  /// The hash value for the range.
-  ///
-  /// Two ranges that are equal will always have equal hash values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {

stdlib/public/core/CollectionOfOne.swift

@@ -148,12 +148,6 @@ extension CollectionOfOne : Equatable where Element : Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension CollectionOfOne : Hashable where Element : Hashable {
-  /// The hash value for the collection.
-  ///
-  /// Two collection that are equal will always have equal hash values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {

stdlib/public/core/Dictionary.swift

@@ -1448,12 +1448,6 @@ extension Dictionary: Equatable where Value: Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension Dictionary: Hashable where Value: Hashable {
-  /// The hash value for the dictionary.
-  ///
-  /// Two dictionaries that are equal will always have equal hash values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {

stdlib/public/core/ExistentialCollection.swift.gyb

@@ -1260,13 +1260,6 @@ extension AnyCollection : Equatable where Element : Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension AnyCollection : Hashable where Element : Hashable {
-  /// The hash value for the collection.
-  ///
-  /// Two `AnyCollection` values that are equal will always have equal hash
-  /// values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {

stdlib/public/core/Mirror.swift

@@ -777,13 +777,6 @@ extension DictionaryLiteral: Equatable where Key: Equatable, Value: Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension DictionaryLiteral: Hashable where Key: Hashable, Value: Hashable {
-  /// The hash value for the collection.
-  ///
-  /// Two `DictionaryLiteral` values that are equal will always have equal hash
-  /// values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {

stdlib/public/core/Optional.swift

@@ -411,7 +411,7 @@ extension Optional : Equatable where Wrapped : Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension Optional : Hashable where Wrapped : Hashable {
-  /// The hash value for the optional.
+  /// The hash value for the optional instance.
   ///
   /// Two optionals that are equal will always have equal hash values.
   ///

stdlib/public/core/Range.swift

@@ -400,12 +400,6 @@ extension Range: Equatable {
 
 @available(swift, introduced: 4.1) // FIXME(conformance-availability)
 extension Range : Hashable where Bound : Hashable {
-  /// The hash value for the range.
-  ///
-  /// Two ranges that are equal will always have equal hash values.
-  ///
-  /// Hash values are not guaranteed to be equal across different executions of
-  /// your program. Do not save hash values to use during a future execution.
   @_inlineable // FIXME(sil-serialize-all)
   @available(swift, introduced: 4.1)
   public var hashValue: Int {