Revert "Make emacs show when clang-format encountered a syntax error."

This reverts commit 236854, which caused clang-format to always print
'{ "IncompleteFormat": false }' at the top of an incompletely formatted file.
This output causes problems e.g. in Polly's automatic formatting checks. Daniel
tried to fix this in 236867, but this fix had to be reverted due to buildbot
failures. I revert this change as well for now as it is Friday night and
unlikely to be fixed immediately.

llvm-svn: 236908