clang-replace: Delete change description files

Added a command line option "-remove-change-desc-files" that triggers
the deletion of the change description files after merging and applying
regardless of success.

Differential Revision: http://llvm-reviews.chandlerc.com/D1492


git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@189268 91177308-0d34-0410-b5e6-96231b3b80d8