[build] Remove gyp usage from landmines script

References from client projects to removed methods have been removed in
previous CLs.

Bug: 756691
Change-Id: I405ec09301455884f00348aadf82e865e85df721
Reviewed-on: https://chromium-review.googlesource.com/925683


Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537929}