Remove references to gyp from DEPS and docs

Bug: 826218
Change-Id: I176e1aeb0b24b21c6b4e5ee40910dce2bce52c95
Reviewed-on: https://chromium-review.googlesource.com/1239461
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#593522}
19 files changed