Having added some entries to an stignore file, I’d now like to ‘tidy up’ the remote destinations.
Where I can go remove directories without too much hassle, the more complicated patterns mean that I might end up deleting files that I shouldn’t, so I’m not reclaiming space I could otherwise reclaim.
If there was an easy way to do a ‘find --ignored-files -print0 | xargs -0 rm’ then that would work, but right now the find portion is the bit that’s missing 
There is nothing like that, so sadly you’ll have to do it by hand.
Ignored files aren’t always files you want deleted, sometimes its files you don’t want others to see, but you don’t want them deleted.
Depending on your situation and which possibilities you have, you could mount two samba shares remotely and then use tools like total commander or syncback free, set your ignore list in the third-party tool, compare and choose to delete what “hangs over”. But be careful not deleting the wrong files on the wrong side.