Revert "upgrade review-dev from gerrit ver 2.4.x to ver 2.8"

We tried, but something in the DB seemed to break schema migrations
so let's undo this for now while we focus testing on that part
specifically. Once that hurdle is past, we can revert this revert to
try again.

This reverts commit 7011082193da25fb30d95f057c7babd9c46d10f0.

Change-Id: I5f6628c1e4366184ac5b4f72c5aaf43207942bf9
Merge "Revert "upgrade review-dev from gerrit ver 2.4.x to ver 2.8""