[clang-tidy] Clean up code after applying replacements.

Summary:
Remove empty namespaces and initializer list commas / colons in
affected ranges. Initial patch: proper options for enabling the cleanup and
specifying the format style are needed.

Reviewers: hokein, ioeric

Subscribers: beanz, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D24572

llvm-svn: 284399