Remove extensions on ImplicitlyUnwrappedOptional from the stdlib.

Extensions on ImplicitlyUnwrappedOptional are not actually accessible
because we force the optional (and thus can only access things on the
type it is wrapping).

Remove these from the stdlib in order to pave the way toward fully
implementing SE-0054.

Author: rudkx

stdlib/public/core/ImplicitlyUnwrappedOptional.swift

@@ -49,73 +49,3 @@ public enum ImplicitlyUnwrappedOptional<Wrapped> : ExpressibleByNilLiteral {
     self = .none
   }
 }
-
-extension ImplicitlyUnwrappedOptional : CustomStringConvertible {
-  /// A textual representation of the value, or `nil`.
-  @_inlineable // FIXME(sil-serialize-all)
-  public var description: String {
-    switch self {
-    case .some(let value):
-      return String(describing: value)
-    case .none:
-      return "nil"
-    }
-  }
-}
-
-/// Directly conform to CustomDebugStringConvertible to support
-/// optional printing. Implementation of that feature relies on
-/// _isOptional thus cannot distinguish ImplicitlyUnwrappedOptional
-/// from Optional. When conditional conformance is available, this
-/// outright conformance can be removed.
-extension ImplicitlyUnwrappedOptional : CustomDebugStringConvertible {
-  @_inlineable // FIXME(sil-serialize-all)
-  public var debugDescription: String {
-    return description
-  }
-}
-
-#if _runtime(_ObjC)
-extension ImplicitlyUnwrappedOptional : _ObjectiveCBridgeable {
-  @_inlineable // FIXME(sil-serialize-all)
-  public func _bridgeToObjectiveC() -> AnyObject {
-    switch self {
-    case .none:
-      _preconditionFailure("Attempt to bridge an implicitly unwrapped optional containing nil")
-
-    case .some(let x):
-      return Swift._bridgeAnythingToObjectiveC(x)
-    }
-  }
-
-  @_inlineable // FIXME(sil-serialize-all)
-  public static func _forceBridgeFromObjectiveC(
-    _ x: AnyObject,
-    result: inout ImplicitlyUnwrappedOptional<Wrapped>?
-  ) {
-    result = Swift._forceBridgeFromObjectiveC(x, Wrapped.self)
-  }
-
-  @_inlineable // FIXME(sil-serialize-all)
-  public static func _conditionallyBridgeFromObjectiveC(
-    _ x: AnyObject,
-    result: inout ImplicitlyUnwrappedOptional<Wrapped>?
-  ) -> Bool {
-    let bridged: Wrapped? =
-      Swift._conditionallyBridgeFromObjectiveC(x, Wrapped.self)
-    if let value = bridged {
-      result = value
-    }
-
-    return false
-  }
-
-  @_inlineable // FIXME(sil-serialize-all)
-  public static func _unconditionallyBridgeFromObjectiveC(_ source: AnyObject?)
-      -> Wrapped! {
-    var result: ImplicitlyUnwrappedOptional<Wrapped>?
-    _forceBridgeFromObjectiveC(source!, result: &result)
-    return result!
-  }
-}
-#endif