Remove deprecated code use (Drupal core 9.3.0 onward)

I think this is the follow-up I suggested in another ticket, thanks for that. I changed the issue title, because this is resolving deprecations, not supporting Drupal 9.3; the latter suggests the module does not work without this patch. Actually, merging these changes would make the module incompatible with Drupal 9.2, so that would have to wait until D9.2 is no longer supported. Lastly, because of that, I also think the info.yml needs an update to denote that the module is only compatible with D9.3+.

This will need work, although certain aspects of the patch will still apply others won't - please raise an MR. (Appreciate its old!)

Ive reviewed these changes, they're not applicable anymore as far as I can tell.