[clang-move] ClangMoveTests: Remove dots in output paths

Summary:
Following D48903 ([VirtualFileSystem] InMemoryFileSystem::status: Return
a Status with the requested name), the paths output by clang-move in the
FileToReplacements map may contain leading "./".  For example, where we
would get "foo.h", we'll now get "./foo.h".  This breaks the tests,
because we are doing exact string lookups in the FileToFileID and
Results maps (they contain "foo.h", but we search for "./foo.h").

To mitigate this, try to normalize a little bit the paths output by
clang-move to remove that leading "./".

This patch should be safe to merge before D48903, remove_dots will just
be a no-op.

Reviewers: ilya-biryukov, hokein

Reviewed By: hokein

Subscribers: ioeric, cfe-commits

Differential Revision: https://reviews.llvm.org/D48951

llvm-svn: 336358