Errors spawn in Console after deleting an effect that had exposed parameters.

To reproduce:
- Open attached project and launch "test" scene
- Open "Ambience" Audio Mixer
- Add an effect to any of the Audio Groups
- Expose some paramters on the effect
- Delete the effect
- Observe that you will now see this messages everytime you click the "Edit in Play Mode" button

m_ExposedParameterCache.size () == GetMixerConstant ()->exposedParameterCount
UnityEditor.DockArea:OnGUI()

- And this error message when you Unexpose the missing effect parameters:

m_ExposedParameterCache.size () == GetMixerConstant ()->exposedParameterCount