Add clang-tidy check to remove redundant .get() calls on smart pointers.

Summary:
This check finds and removes redundant .get() calls on smart pointers.
Example:
  ptr.get()->Foo()   ==>   ptr->Foo()

Reviewers: alexfh

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D3186

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@204947 91177308-0d34-0410-b5e6-96231b3b80d8