Remove unused anchor-target CSS for Conpherence message pane
Summary:
Remove unused CSS selectors related to `anchor-target` which do not get applied due to missing a whitespace.
Even when making them apply, they do not add any value apart from a small yellow square placed in an unhelpful spot.
See also https://we.phorge.it/D25992 for gory details.
Test Plan: Go to a Conpherence chat via an anchor link like `Z1#10`, inspect HTML's CSS classes for messages at top of the room (setting policy etc) and also posted chat messages themselves. See no visual differences.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Differential Revision: https://we.phorge.it/D25992