How to reproduce:
1. Open the attached "UnityAnimatorEvents.zip" Project
2. Open the "test controller" in the Animator window
3. Click on the "New State"
4. Add any script as a behavior several times (to see the difference)
5. Save and check "test controller.controller" file size in the file explorer
6. In the debug inspector change State Machine Behaviour Size array to 0
7. Save and check the size of the "test controller.controller" file again

Expected Behaviour: The State behaviours are cleaned up as some of them are not used
Actual Behaviour: The State behaviours are not cleaned up after setting the array to 0

Reproducible with: 2017.4.32f1, 2018.4.7f1, 2019.2.2f1, 2019.3.0a12, 2019.3.0a12, 2020.1.0a1