refactor(snack-bar): remove overly broad animation variables (#10405)
refactor(snack-bar): remove overly broad animation variables (#10405)

Removes the `SHOW_ANIMATION` and `HIDE_ANIMATION` variables from the snack bar which were being exported all the way up to `@angular/material` and were implying that these are generic show and hide animations.

BREAKING CHANGES:
* `SHOW_ANIMATION` has been removed.
* `HIDE_ANIMATION` has been removed.
josephperrott/material2,DevVersion/material2,ppham27/material2,andrewseguin/material2,amcdnl/material2,amcdnl/material2,andrewseguin/material2,DevVersion/material2,mmalerba/material2,tinayuangao/material2,crisbeto/material2,DevVersion/material2,angular/components,crisbeto/material2,mmalerba/material2,ppham27/material2,andrewseguin/material2,tinayuangao/material2,jelbourn/material2,crisbeto/material2,jelbourn/material2,angular/components,josephperrott/material2,andrewseguin/material2,Jefiozie/material2,mmalerba/material2,tinayuangao/material2,DevVersion/material2,ppham27/material2,Jefiozie/material2,ppham27/material2,mmalerba/material2,jelbourn/material2,ppham27/material2,Jefiozie/material2,mmalerba/material2,Jefiozie/material2,amcdnl/material2,josephperrott/material2,Jefiozie/material2,amcdnl/material2,josephperrott/material2,josephperrott/material2,amcdnl/material2,tinayuangao/material2,DevVersion/material2,jelbourn/material2,crisbeto/material2,tinayuangao/material2,jelbourn/material2,angular/components,andrewseguin/material2,angular/components