Remove unnecessary Cinder v1 code

Since the commit I04de2d90fe11f8ec4acbfa983bc0ad3aa979f45b Cinder v1
API tests have been removed. So there is not any case which requires
_api_version is 1. This patch just removes it.

TrivialFix

Change-Id: I7af71ef6eada3017bc5a96830515915b7a848a74
1 file changed