How did you define them in the first place?
*.items files or via the PaperUI Simple Mode for Item Linking?
It seems that you used PaperUI, so you should have followed another sequence to clear your OH2 system from the old info.
First, you delete the links from the channels, then delete the Items, then delete the Things.
Since you removed the Thing first, you are left with orphan links and items in your system.
To remove those, you could use the openHAB console and:
smarthome:links list |grep -i mpower
This command will show you the links between the Items and the Channels of the Things.
You can delete the links with
smarthome:links removeChannelLink <itemName> <thingUID>
Then, you can also delete the old Items with:
smarthome:items remove <itemName>