Once you have created and named a Position Group, you can delete it at any time so that shortcut will not appear in the Positions dropdown menu.

Delete a Position Group:
From any Schedule Page: 

• In the Positions dropdown, choose Select/Group Positions
• In the Select Positions window, scroll down to the bottom Existing Position Groups section
• Click the Delete link next to the Position Group 
• The window will close and the group will no longer appear in the Positions dropdown