gerrit: remove one replication to gallium

We replicate the Gerrit repositories on gallium to two directories:

 /srv/ssd/gerrit
 /var/lib/git

The later is no more needed, all scripts/jenkins jobs are now pointing
to /srv/ssd/gerrit.

Feel free to merge / deploy at anytime.  Will clean up gallium whenever
the change has been deployed.

Bug: 63937
Change-Id: I0d1c933afe3cb7a213e19dcd61ce25cf0571811e
Merge "gerrit: remove one replication to gallium" into production