Drop the adding and removing of the 'running' class in SVGTestCase.js

This class will trigger layouts that could hide the intended effects of
the tests using this "framework". Since the same elements are marked as
being hidden, this will not affect the graphical output.

BUG=231560

Review-Url: https://codereview.chromium.org/2104943005
Cr-Commit-Position: refs/heads/master@{#404380}
1 file changed