Clean up openstack-common.conf

This patch clean up unused module and wrong module name.
The issues are detected by new change about update.py
in I68c0108304be8a315bcefe939c22019caab9bc98. This patch
doesn't depend the oslo-incubator patch.
 * remove unused module sslutils, versionutils
 * fix wrong module db.sqlachemy in openstack-common.conf

Change-Id: I55affbb398d97b1da8c15576ae1c54f27e6ad714