fate/filter: stick delogo test with its deps (cosmetics).
fate/filter: rename 'ubitux' rules to 'sample'.
fate/filter: remove pointless indirections for gradfun and hqdn3d.
fate/filter: move some CMD below deps for consistency.
fate/filter: move concat filtergraph to a dedicated script.
fate/filter: move gradfun filtergraph to a dedicated script.
fate/filter: make overlay test bitexact.