IsDeselectAllActive was identical to IsDeselectAll (both return the
deselectAll flag under a read lock). The two were introduced in parallel
on separate branches for the same fix - guarding against management route
sync overriding a user's explicit deselect-all - and ended up coexisting
after the branches merged.
Drop IsDeselectAllActive, keep the canonical IsDeselectAll from main, and
move its richer doc comment over. Update callers accordingly.
2d54c7f088