Kill [stdlib] attribute.

Now that we have true serialized modules, the standard library can import
the Builtin module without any special direction (beyond -parse-stdlib),
and anyone can include those modules without special direction.

Swift SVN r6752

include/swift/AST/ModuleLoader.h

@@ -39,16 +39,11 @@ public:
   /// \param path A sequence of (identifier, location) pairs that denote
   /// the dotted module name to load, e.g., AppKit.NSWindow.
   ///
-  /// \param isStdlibImport True if this is a [stdlib] import.  FIXME: this
-  /// should be removed when we have real binary modules and/or build system
-  /// support.
-  ///
   /// \returns the module referenced, if it could be loaded. Otherwise,
   /// emits a diagnostic and returns NULL.
   virtual
   Module *loadModule(SourceLoc importLoc,
-                     ArrayRef<std::pair<Identifier, SourceLoc>> path,
-                     bool isStdlibImport) = 0;
+                     ArrayRef<std::pair<Identifier, SourceLoc>> path) = 0;
 
   /// \brief Look for declarations associated with the given name.
   ///