Redirectors
Moving or renaming an asset in UE4 leaves a Redirector in its old location. This is so that packages that are not currently loaded, but reference this asset, will know where to find it in its new location.
Seeing Redirectors in the Editor
Enable Filters->Other Filters->Show Redirectors to fix up Redirectors individually and see them in your content folder:
Right clicking a Redirector and selecting Fix Up will resave all packages that point to the Redirector, and will delete the Redirector if it was able to resave all things referencing it.