Remove output that's no longer generated from inspector_instrumentation_sources

This is breaking Official Canary/Dev because it causes a re-run of
inspector_instrumentation_sources on every build, which breaks the
syzygy relink steps.

BUG=342974
R=abarth@chromium.org, chrisha@chromium.org, sebmarchand@chromium.org
TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/144463017

git-svn-id: svn://svn.chromium.org/blink/trunk@166947 bbb929c8-8fbe-4397-9dbb-9b2b20218538