Here are the steps to remove ad hoc network from Windows 7
1. Click ‘Start’ and select ‘Control Panel’.
2. In the View by: category drop down select Small icons.
3. Click on Network and Sharing Center
4. On the top left click on Manage wireless networks.
5. Select the ad hoc Network you wish to delete right click and select remove network.
6. A warning message will come up asking you if you are sure? click yes to confirm.
That is it your ad hoc should be deleted.