SQLALCHEMY_DATABASE_DRIVER is no longer used
after If6d8d08e5b7b7c48ca012677b536d71058def6fd .
Also, remove mysql connector packages from the install list.
Closes-Bug: #1523377
Related-Bug: #1493304
Change-Id: I5ecbc3b0bac989faa5c46d3c2866558a505414d8