Remove cinder/compute/aggregate_states.py

This file is from the initial fork from nova. It defines the states a
host aggregate can take. It is not used anywhere in the cinder code
and is therefore unnecessary.

The commit removes the file from the codebase.

Change-Id: I9ba12aabc5009020950b746f312372fa4bfa156d
Merge "Remove cinder/compute/aggregate_states.py"