Cleanup tools after M

Remove the reference to preview_sources from gyp file and also delete
the unnecessary sources.

BUG=512264

Change-Id: Ia258dcb5d0625cc75a4f9d143448fd707f0d0af0
Reviewed-on: https://chromium-review.googlesource.com/305881
Commit-Queue: Selim Gurun <sgurun@chromium.org>
Reviewed-by: Aurimas Liutikas <aurimas@chromium.org>
Commit-Queue: Aurimas Liutikas <aurimas@chromium.org>
Tested-by: Aurimas Liutikas <aurimas@chromium.org>