Please note this is a channel-specific article only applicable to eBay.
The Channel Mapping screen for eBay is showing old SKUs that are no longer used on eBay.
The Channel Mapping screen receives information about which listings to display directly from the channel, however, the information displayed there will only be appended and there is no way for the system to know which SKUs to not display any longer if they have been changed/deleted from the channel. The records that have been present earlier during any syncs with the channel will still display later on.
If you wish to clean up your Channel Mapping screen for eBay to not display any old/outdated SKUs any longer, you can use the eBay Strike Off feature. Please see here for full details on accessing and using the feature. Also, note that strike off can be done in bulk via the Strike off eBay listing import, however, the import would not work if you wish to strike off only certain child SKUs from a variation listing. To strike off individual child SKUs you would need to use the feature described in the aforementioned documentation.