Remove "static:" element type from animation-test-helpers.js

Currently animation-test-helpers.js supports prefixing element ids with
"static:". This patch removes this prefix as we just just remove them
and do nothing differently.

Review URL: https://codereview.chromium.org/693613006

git-svn-id: svn://svn.chromium.org/blink/trunk@185147 bbb929c8-8fbe-4397-9dbb-9b2b20218538