Remove "Updated" view from Differential

Summary:
This landed during my review drama embargo and is a generally good idea but had
some implementation issues.

@elynde reports it has been broken for some time, although it still works on
secure.phabricator.com so I'm guessing it's just taking a zillion years to run
at Facebook. It's up to more than a second for me on secure.phabricator.com:

https://secure.phabricator.com/file/view/PHID-FILE-v4ql4c66u3xnkarmrpm4/

The basic problem is that some of the data architecture around this
implementation is hard to scale. I want to pursue a similar feature eventually,
but drive it off notifications that we'll ship through real-time infrastructure
too.

I'm also trying to get rid of DifferentialRevisionListData and this simplifies
that somewhat.

Test Plan:

• Grepped for table name, table constant, query constant, and class name; no

hits.

• Applied SQL patch.
• Verified that Differential no longer shows "Updated".

Reviewers: elynde, btrahan, jungejason

Reviewed By: elynde

CC: aran, elynde

Differential Revision: 1178