clang-format.py: Don't omit the first two words from error messages.

This reverts r172072.  clang-format used to use DiagnosticEngine to output
errors: http://llvm.org/viewvc/llvm-project?view=revision&revision=172071. Now
it doesn't, so this code is obsolete.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206479 91177308-0d34-0410-b5e6-96231b3b80d8