refactor(ngAnimate): simplify functions and remove redundant args/calls

Simplifies/Optimizes the following functions:

- `areAnimationsAllowed()`
- `cleanupEventListeners()`
- `closeChildAnimations()`
- `clearElementAnimationState()`
- `markElementAnimationState()`
- `findCallbacks()`

Although not its primary aim, this commit also offers a small performance boost
to animations (~5% as measured with the `animation-bp` benchmark).