Remove WrapperMatcherInterface

Summary:
WrapperMatcherInterface is an abstraction over a member variable -- in
other words, not much of an abstraction at all. I think it makes code
harder to read more than in helps with deduplication. Not to even
mention the questionable usage of the ~Interface suffix for a type with
state.

Reviewers: ymandel

Reviewed By: ymandel

Subscribers: arichardson, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D80704