Fix "unused variable" warnings.

These were exposed by changing DISALLOW_COPY_AND_ASSIGN to use "= delete", and
must be fixed before that change can land.

See https://codereview.chromium.org/1981053002/ for the full CL.

BUG=447156
TEST=none
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/1995983002
Cr-Commit-Position: refs/heads/master@{#395452}
33 files changed