From the WHS console, storage tab remove the disk that you physically removed. When finished your files should be accessible again through the shares.
Please note, if the disk you physically removed also contained (part of) your client backup database you may permanently loose all current client backups since these files aren't duplicated. If you don't need any files from these backups this should be no
problem, you will however need to repair the client backup database and then run backup again for all clients.
If you want to know for sure if there any client backups on this disk simply mount the disk in a client and check if a folder named .\DE\folders\{00008086-058D-4C89-AB57-A7F909A47AB4} is present (please note you need to have "view hidden files
and folders" enabled to be able to see the hidden DE folder in the root of the drive)