cpp11-migrate: Use Replacement serialization from clang::tooling

Serialization of replacements has been moved to clang::tooling.

Differential Revision: http://llvm-reviews.chandlerc.com/D1423



git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@188820 91177308-0d34-0410-b5e6-96231b3b80d8