The spirv_tools_external_revision_generate action should no longer
depend on ANGLE's DEPS file exclusively. We're using the version of
SPIRV-Tools provided by Chromium or ANGLE depending on the client.

Depending on DEPS directly should give the correct behaviour.

Bug: chromium:926354
Change-Id: I87ac59f1e3f0d3a0b13df51fb6477940ff534dc7
Reviewed-on: https://chromium-review.googlesource.com/c/1446495Reviewed-by: Nico Weber <thakis@chromium.org>