Remove unused db_sync from extensions

The db_sync in the extensions isn't used, either by the tests or
by keystone-manage db_sync, so remove them.

Change-Id: Ia0598e8dae81e258a05767f47525d5c11acce8db
Keystone doesn't use pam

The requirements.txt file had pam, but Keystone doesn't use pam.

Change-Id: Ib617146d4ec75532f994ae85837ecbf383647306
Merge "Remove unused db_sync from extensions"
Merge "Keystone doesn't use pam"