Remove selection indicator from the reader bottom sheet.

As part of the Information Architecture project we are adding a filter to select different streams of posts in the reader. The filter is implemented with a bottom sheet and the main PR is this one.

While reviewing it, it has been noticed a possible UX issue when re-selecting an already selected filter (see this comment for more context).

Two possible routes highlighted by Chris:

1. Treat it as a check box. Show a selected state. Tapping on the selected state unselects it. But in this case, I think the sheet should stay open. Currently the sheet closes on any selection, so its more like a quick switcher between sites.
2. Removing the selected indicator could make it feel less like a checkbox/radio button and more like a shortcut.
   ...
   ...if I was to make a change I would actually do the second one, and not show a selected indicator

cc @osullivanchris and @malinajirka

Start by reviewing PR #11193 and the reader bottom-sheet implementation it introduces, then check the linked UX discussion for the intended behavior. Done means the selected filter no longer shows a selection indicator in the bottom sheet while the existing stream-selection flow remains intact.