ancil variables not being correctly removed from filter commands in UKESM1-3-LL

[matthew-mizielinski]

Some issues with masks not being picked up;

+ tauuo_tavg-u-hxy-sea : ocean           constraint: [{'variable_name': 'tauuo', 'substream': 'grid-U'}, {'variable_name': 'mask_3D_U', 'substream': 'grid-U'}]   - embargoed
 + tauvo_tavg-u-hxy-sea : ocean           constraint: [{'variable_name': 'tauvo', 'substream': 'grid-V'}, {'variable_name': 'mask_3D_V', 'substream': 'grid-V'}]   - embargoed