fix($animate): ensure transition-property is not changed when only keyframe animations are in use

[matsko]

Closes #3933

[mary-poppins]

Thanks for the PR!

• Contributor signed CLA now or in the past
  • If you just signed, leave a comment here with your real name
• PR's commit messages follow the commit message format

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!

[btford]

Landed as 2df3c9f.

[matsko]

Thanks Brian!