Discontinue comment visibility strategy for new change screen

As explained in this change [1] comment visibility strategy is replaced
by autoOpen(lastReply) strategy and is going to be removed (also from the
database), when old change screen is removed. Mark label for this setting
on my preference screen as "Old Change Screen" only.

[1] https://gerrit-review.googlesource.com/55536

Bug: Issue 2456
Change-Id: I1b36e9d53a8f35ff0f8f1fb793d3082fb5669452
Merge "Discontinue comment visibility strategy for new change screen" into stable-2.9