Revert "Foundation overlay: add String.stringByApplyingTransform()"

Speculatively reverted because of iOS bot failure.

Swift SVN r28261

stdlib/public/SDK/Foundation/NSStringAPI.swift

@@ -1468,13 +1468,5 @@ extension String {
     try self._ns.writeToURL(
       url, atomically: useAuxiliaryFile, encoding: enc)
   }
-
-  @availability(iOS, introduced=9.0)
-  @availability(OSX, introduced=10.11)
-  public func stringByApplyingTransform(
-    transform: String, reverse: Bool
-  ) -> String? {
-    return _ns.stringByApplyingTransform(transform, reverse: reverse)
-  }
 }