Remove db_enforce_mysql_charset option for db_sync of glance-manage

This is a deprecated option only should be used for migration. As we
scheduled before, now glance removes it out from Juno release.

Change-Id: Ice4ade659307ee5e635a75d6637b4664ee431c20
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Remove db_enforce_mysql_charset option for db_sync of glance-manage"