RCFilters: Fix validation for single_option groups

RCFilters: Fix validation for single_option groups

The single_option groups have a base definition that means they
always must have a value, and must never have more than one value.
The previous way we attempted to do that was confusing and missed
a case where after resetting filters, two values were selected before
one could be unselected, which then broke the behavior in the
entire group.

This fix reorganizes the validation when an item in the group is
selected or unselected to make sure the group retains its promised
behavior.

Bug: T173303
Change-Id: I5758ec324a26c0e5e6f5c473d206e818a1d22523