Revert "Make sure we always de-serialize transparent functions."

This reverts commit 821b365054.

It caused a bunch of execution time regressions.

include/swift/SIL/SILModule.h

@@ -130,9 +130,6 @@ private:
   llvm::StringMap<SILFunction *> FunctionTable;
   llvm::StringMap<SILFunction *> ZombieFunctionTable;
 
-  /// The last function which was handled in linkTransparentFunctions().
-  SILFunction *LastFunctionChecked = nullptr;
-
   /// The list of SILFunctions in the module.
   FunctionListType functions;
 
@@ -246,12 +243,6 @@ public:
   /// Invalidate cached entries in SIL Loader.
   void invalidateSILLoaderCaches();
 
-  /// De-serializes all transparent functions for which there is only a
-  /// declaration yet (meaning: the body was not de-serialized yet).
-  ///
-  /// See also: SILFunction::Transparent.
-  void linkTransparentFunctions();
-
   /// Erase a function from the module.
   void eraseFunction(SILFunction *F);