Revert "Add default_volume_type as cinder api parameter"

This parameter is already managed by cinder::backends.

If it should be moved to cinder::api, a new change should be proposed.

This reverts commit cd7391c5e2567a081d5a214a80cb773caa1ae2c6.

Change-Id: I52e2b296be81db2e085bb3403b95bcb48d081821
Merge "Revert "Add default_volume_type as cinder api parameter""