fix($animate): prevent leaving animate classes after animation is done

[jrencz]

In some cases ngAnimate transitional classes (like *-remove & *-remove-active) were left after animation was over. Change introduced in this commit prevent such situations.

Closes #4490

[mary-poppins]

Thanks for the PR!

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Thanks again for your help!

[jrencz]

Jarosław Rencz