Revert r143342. Caching of code-completion results was intentionally placed in "reparse"

because we don't want to take this performance hit when doing code completion

Log of r143342:
Move caching of code-completion results from ASTUnit::Reparse to ASTUnit::CodeComplete,
so that it will happen when we are doing code-completion, not reparsing.

llvm-svn: 143367