R1:42a8b73adbaa

Feed Differential retitled: do not repeat the title twice

Summary:
This is a cosmetic modification for a specific Feed.

https://we.phorge.it/T15183

If you retitle a Diff (and you do nothing else), its Feed
is somehow too much verbose:

... retitled NEW_TITLE from OLD_TITLE to NEW_TITLE

In this specific case, the Feed now becomes shorter so that
the NEW_TITLE is not repeated twice:

... retitled NEW_TITLE from OLD_TITLE

Note that, if the title changes again, the Feed naturally comes
back as…