WebUI: make polymer's reproduce.sh clean up excluded files.

Files that were in rsync_exclude.txt were just ignored and left in the
codebase. This CL makes the reproduce script clean up the excluded files.

Bug: 843350, 902959
Change-Id: I99d2147cb0f73d51dd9fe4443b5ce677e4d37d37
Reviewed-on: https://chromium-review.googlesource.com/c/1380938
Commit-Queue: Scott Chen <scottchen@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#617284}
19 files changed