Steps to reproduce:

1. Open the attached project
2. Look at the three animator controllers (Assets/animators/). Notice 'tpac-original' is the same as 'tpac-test'.
3. Open the 'tpac-test' controller and delete 'test-subsm' sub-state machine, notice 'tpac-test' is now identical to 'tpac-empty' controller
4. Open the assets folder in file explorer and inspect animator controller memory sizes, notice 'tpac-empty' takes about 3KB of space, while 'tpac-test' takes around 20KB even though they are now completely same controllers.