It would be most straightforward to let them sync and then delete them. However, if you did any work on these photos in Lightroom mobile, then it will be the copies that are syncing that you'll want to keep, not the ones from your One Drive.
If you want to stop them from syncing, however, then delete them from Lightroom Photos on your mobile device. Photos that have already uploaded to the cloud, however, will still sync. The only way to delete these before they arrive on your computer is to go, in Lightroom desktop, into Preferences, and on the Lightroom mobile tab, Delete All Data. This will delete all that is in the cloud - the photos you're referring to, but also all that you have synced from Lightroom desktop to your mobile device. (They will be resynced, however.)
In the future, either don't import the images into Lightroom mobile, or don't import copies from your One Drive into Lightroom desktop. One of the strengths of Lightroom mobile is that all that is imported into it will automatically arrive in Lightroom desktop.
That's amazing! They only documentation I could ever find on anything said LRM would only store small, compressed images in the cloud. Had no idea it would save the RAW originals for me until I got to my computer.
I will let it download then. Thanks so much!
You're welcome. Lightroom mobile has gotten some great improvements, including this ability. Before deleting anything though, verify - are the copies being synced in fact raw files?
Note that what you read is still true going in the opposite direction - when you sync photos from Lightroom desktop to Lightroom mobile, it is only small compressed raw files ("smart previews") that are synced up to the cloud and down to your mobile device.