gclient: remove support for $matching_files in hooks
gclient: remove support for $matching_files in hooks

This feature seems to be unused, and removing it will
simplify handling hooks a little bit.

Bug: 661382
Change-Id: I89f28dedb7f59cd475b176cfb1f023094520d6b7
Reviewed-on: https://chromium-review.googlesource.com/509614
Reviewed-by: Dirk Pranke <6693ee08b084bb2ffa767f664c99b689395e0e4b@chromium.org>
Commit-Queue: Paweł Hajdan Jr. <84cab74a96a175cf90ed68b8abab420352923e11@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools