Revert "Improve error recovery around colon."

This reverts commit r212957.  It broke the self-host on code like this
from LLVM's option library:
  for (auto Arg: filtered(Id0, Id1, Id2))

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212965 91177308-0d34-0410-b5e6-96231b3b80d8