Fix //testing import lint issues

Removes the import-related entries from //testing's pylintrc file and
fixes resulting lint errors.

Bug: 353942917
Change-Id: Ie3b3dba795e0806631c37243a3b4f480a4215a6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5737567
Auto-Submit: Brian Sheedy <bsheedy@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1337485}
NOKEYCHECK=True
GitOrigin-RevId: a418670f47e2a8bb3a2ce69e990203eb69b5225f