Revert "Just call getContextDescriptor to get the context for subprograms"
while I investigate as it seems to be causing issues with the gdb bot.

This reverts commit r204874.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@204896 91177308-0d34-0410-b5e6-96231b3b80d8