Revert r347627 "[MS] Push fewer DeclContexts for delayed template parsing"

It broke the Windows self-host:
http://lab.llvm.org:8011/builders/clang-x64-windows-msvc/builds/1799/steps/stage%202%20build/logs/stdio

I can build
lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/MachinePostDominators.cpp.obj to
repro.

llvm-svn: 347630