chore(ngAnimate): cleanup vendor prefixes handling in tests

1. Change all transition/transform/animation-related ss.addRule to
   ss.addPossiblyPrefixedRule to account for the -webkit- prefix.
2. Remove manually added -webkit-prefixed rules in favor of automatically
   handling them in ss.addPossiblyPrefixedRule.

Closes #15406

Author: mgol