Remove GYP execution from DEPS hooks (gclient {sync,runhooks})

Due to the recent roll of chromium_revision in DEPS in
https://codereview.webrtc.org/2269953002/ an Android checkout
now experiences an error when running GYP (which is automatically
done as a hook when you run 'gclient {sync,runhooks}'.

This CL removes the GYP invocation entirely, as it would soon be
removed anyway as part of the GN migration.

All our bots are executing GYP/GN as part of the MB step
(called 'generate_build_files'), so they won't be affected.

BUG=webrtc:5949,webrtc:6258
NOTRY=True

Review-Url: https://codereview.webrtc.org/2280633002
Cr-Commit-Position: refs/heads/master@{#13920}

DEPS

@@ -83,12 +83,5 @@ hooks = [
                '--bucket', 'chromium-webrtc-resources',
                'src/resources'],
   },
-  {
-    # A change to a .gyp, .gypi, or to GYP itself should run the generator.
-    'name': 'gyp',
-    'pattern': '.',
-    'action': ['python', 'src/webrtc/build/gyp_webrtc.py',
-               Var('extra_gyp_flag')],
-  },
 ]