discover: include Remove button in tab chain
The Remove button was excluded from the tab chain many years ago in 07aaf62e. This makes it impossible to get to the button using tab navigation, which wasn't a problem when the button was used as an extra on ListView cards that users could access through the application's full page. But now that we use it also on that page, we need to have it included or the button isn't accessible either.
Instead, we include the button in the tab chain when it's used on the app's page. We still leave it out for ListViews, as having potentially hundreds of delegates included is very cumbersome (and doesn't even work well), though we may want to adjust this in the future to include the button if and only if it is on the currently selected delegate.
BUG: 505544 FIXED-IN: 6.4.1