[clang-tidy] Cleanup namespace in utils folder.

Summary:
This is a step forward cleaning up the namespaces in clang-tidy/utils.
There is no behavior change.

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D19819

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@268356 91177308-0d34-0410-b5e6-96231b3b80d8
30 files changed