postgresql: Update setup-disks to not move /tmp.

Drop the change to move `/tmp` onto the local disk.  Doing this move
confuses `resolved` until there is a restart, and has no clear
benefits.  The change came in during bf82fadc95, but does not describe
the reasoning; it is particularly puzzling, since postgresql stores
its temporary files under `$PGDATA/base/pgsql_tmp`.

puppet/zulip_ops/files/postgresql/setup_disks.sh

@@ -13,10 +13,6 @@ pg_ctlcluster 9.5 main stop
 mv /var/lib/postgresql /srv
 ln -s /srv/postgresql/ /var/lib
 
-mv /tmp /srv
-mkdir /tmp
-mount --bind /srv/tmp /tmp
-echo "/srv/tmp   /tmp  bind   nofail,defaults,bind 0 0" >> /etc/fstab
 # TODO use systemctl instead of pg_ctlcluster on CentOS
 pg_ctlcluster 9.5 main start