[clang-tidy] Address review comments for the Twine checker.

- Remove unused includes.
- Minor wording fix.
- Added support to check for clang-tidy messages to check_clang_tidy_fix.sh
= Updated test case.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@212540 91177308-0d34-0410-b5e6-96231b3b80d8