Deduplicate sets of replacements by file names.

Summary:
If there are multiple <File, Replacements> pairs with the same file
path after removing dots, we only keep one pair (with path after dots being
removed) and discard the rest.

Reviewers: djasper

Subscribers: klimek, hokein, bkramer, cfe-commits

Differential Revision: https://reviews.llvm.org/D25565

llvm-svn: 284219