[clang-tidy] Cleanups utils files

Summary:
Cleanup some code by using appropriate APIs.
Some coding style cleanups.

There is no behavior changes.

 - Function `IncludeSorter::CreateFixIt` can be replaced by `FixItHint::CreateReplacement`.
 - Function `cleanPath` is a wrapper for `llvm::sys::path::remove_dots`.

Reviewers: alexfh

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D20279

llvm-svn: 269656