clang-format: Remove old hack that mainly made incorrect tests pass.

As a side-effect, constructors definitions will correctly be recognized
and formatted as function declarations. Tests will be added in a
follow-up patch actually using the correct recognition.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194209 91177308-0d34-0410-b5e6-96231b3b80d8