Remove selection indicator from the reader bottom sheet.

[develric]

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

[develric]

This is still current (tested with current develop 16.1-rc-1 on Pixel 3 Emu API 28), so leaving it opened but removing it from IA GH Project that is not currently active.

[stale]

This issue has been marked as stale because:

• It has been inactive for the past year.
• It isn't in a project or a milestone.
• It hasn’t been labeled [Pri] Blocker, [Pri] High, or good first issue.

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