Revert "ClangImporter: Use the new CacheGeneratedPCH in Clang"

This reverts commit da8a1c5.

Author: Davide Italiano

lib/ClangImporter/ClangImporter.cpp

@@ -1451,7 +1451,6 @@ ClangImporter::emitBridgingPCH(StringRef headerPath,
   invocation->getFrontendOpts().ProgramAction = clang::frontend::GeneratePCH;
   invocation->getPreprocessorOpts().resetNonModularOptions();
   invocation->getLangOpts()->NeededByPCHOrCompilationUsesPCH = true;
-  invocation->getLangOpts()->CacheGeneratedPCH = true;
 
   clang::CompilerInstance emitInstance(
     Impl.Instance->getPCHContainerOperations());