I am trying to remove a texture data block from a file. It seems to have been put there by an addon that is no longer installed. The texture block is a Linked block, originally linked in from a file in the addon's folder. Normally you could click the link icon to make it local, then set users to zero. However, the link icon is greyed out, and when highlighted says "Indirect library data-block, cannot change."
The texture's data block also shows up under Orphan Data in the outliner, but all its options are greyed out.
How do I fully delete this?