[stdlib] remove the single-element update functions

- as per an update to the proposal

Author: glessard

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -938,24 +938,6 @@ extension Unsafe${Mutable}BufferPointer {
     p.initialize(to: value)
   }
 
-  /// Updates the initialized element at `index` to the given value.
-  ///
-  /// The memory underlying the destination element must be initialized,
-  /// or `Element` must be a trivial type. This method is equivalent to:
-  ///
-  ///     self[index] = value
-  ///
-  /// - Parameters:
-  ///   - value: The value used to update the buffer element's memory.
-  ///   - index: The index of the element to update
-  @inlinable
-  @_alwaysEmitIntoClient
-  public func updateElement(at index: Index, to value: Element) {
-    precondition(startIndex <= index && index < endIndex)
-    let p = baseAddress._unsafelyUnwrappedUnchecked.advanced(by: index)
-    p.pointee = value
-  }
-
   /// Retrieves and returns the element at `index`,
   /// leaving that element's underlying memory uninitialized.
   ///

stdlib/public/core/UnsafeBufferPointerSlice.swift

@@ -950,24 +950,6 @@ extension Slice {
     base.baseAddress.unsafelyUnwrapped.advanced(by: index).initialize(to: value)
   }
 
-  /// Updates the initialized element at `index` to the given value.
-  ///
-  /// The memory underlying the destination element must be initialized,
-  /// or `Element` must be a trivial type. This method is equivalent to:
-  ///
-  ///     self[index] = value
-  ///
-  /// - Parameters:
-  ///   - value: The value used to update the buffer element's memory.
-  ///   - index: The index of the element to update
-  @inlinable
-  @_alwaysEmitIntoClient
-  public func updateElement<Element>(at index: Index, to value: Element)
-    where Base == UnsafeMutableBufferPointer<Element> {
-    assert(startIndex <= index && index < endIndex)
-    base.baseAddress.unsafelyUnwrapped.advanced(by: index).pointee = value
-  }
-
   /// Retrieves and returns the element at `index`,
   /// leaving that element's underlying memory uninitialized.
   ///

stdlib/public/core/UnsafePointer.swift

@@ -792,22 +792,6 @@ public struct UnsafeMutablePointer<Pointee>: _Pointer {
     update(repeating: repeatedValue, count: count)
   }
 
-  /// Update this pointer's initialized memory.
-  ///
-  /// The range of memory starting at this pointer and covering one instance
-  /// of `Pointee` must be initialized, or `Pointee` must be a trivial type.
-  /// This method is equivalent to:
-  ///
-  ///     self.pointee = value
-  ///
-  /// - Parameters:
-  ///   - value: The value used to update this pointer's memory.
-  @inlinable
-  @_alwaysEmitIntoClient
-  public func update(_ value: Pointee) {
-    pointee = value
-  }
-
   /// Update this pointer's initialized memory with the specified number of
   /// instances, copied from the given pointer's memory.
   ///

validation-test/stdlib/UnsafeBufferPointerSlices.swift

@@ -263,17 +263,12 @@ UnsafeMutableBufferPointerSliceTests.test(
   b[...].initializeElement(at: n, to: s)
   expectEqual(b[n], s)
 
-  a.updateElement(at: n, to: t)
-  expectEqual(a[n], t)
-  b[...].initializeElement(at: n, to: t)
-  expectEqual(b[n], t)
+  expectEqual(a.moveElement(from: n), s)
+  expectEqual(b[...].moveElement(from: n), s)
 
-  expectEqual(a.moveElement(from: n), t)
-  expectEqual(b[...].moveElement(from: n), t)
-
-  a.initializeElement(at: 0, to: s)
+  a.initializeElement(at: 0, to: t)
   a.deinitializeElement(at: 0)
-  b.initializeElement(at: 0, to: s)
+  b.initializeElement(at: 0, to: t)
   b[...].deinitializeElement(at: 0)
 }