If the source does not "touch" any of your current people or have citations to people currently in your file, the easiest way to get rid of all at once should be to delete the source. In the Source Workspace, left panel, find the source, right click, delete source.
However, if that source is still good for people and facts remaining in your tree, you've got a bit of a problem, I think.
The only thing I can think of is to go to the Source Workspace, find the source in the left panel and then, starting at the top of citations listed in the top-middle panel, select each one, one-at-a-time, looking at the number of links in the bottom part of the middle panel. When you find citations to "ghosts", select them and click on the "unlink" chain in the button bar.
PS - citations are not deleted - they are unlinked.
BTW, they are probably not hurting anything by remaining in your file - they just look "messy" when you look in your Source Workspace.
However, if that source is still good for people and facts remaining in your tree, you've got a bit of a problem, I think.
The only thing I can think of is to go to the Source Workspace, find the source in the left panel and then, starting at the top of citations listed in the top-middle panel, select each one, one-at-a-time, looking at the number of links in the bottom part of the middle panel. When you find citations to "ghosts", select them and click on the "unlink" chain in the button bar.
PS - citations are not deleted - they are unlinked.
BTW, they are probably not hurting anything by remaining in your file - they just look "messy" when you look in your Source Workspace.