Node tags: fix removal of tag for a node
Node tags: fix removal of tag for a node

Tag (label link) removal failed when more than one link to the given
label existed, as the node ID was not used in remove_label_link.

Note this patch violates some DRY with label_update. Labels would
benefit from refactoring.

See comment on acardona/CATMAID#869.

fzadow/CATMAID,fzadow/CATMAID,fzadow/CATMAID,fzadow/CATMAID