fix(ngAnimate): class-based animations must not set addClass/removeClass CSS classes on the element

With the abstraction system that ngAnimate uses, $animateCss internally
sets the provided `event` as a CSS class on the element. In this
situation the `addClass` and `removeClass` events on the element as a
CSS class. This should not happen with class-based animations and this
feature is unnecessary and has now been removed.

Closes #11810