Wildcards are just another talkgroup object. Go into either the talkgroups tab on the Trunked systems tab, or the scanlist the wildcard is a member of on the Scanlists tab. Highlight the wildcard object and then click on the delete button.
Now the busy signal is indeed an encrypted transmission. To lock out just that talkgroup that's encrypted so that you can continue searching for new talkgroups, when the talkgroup is active, press the Menu key on the scanner's keypad, then select the store wildcard option. Then lock it out the next time it becomes active. Just pressing the skip button when the wildcard hits will lock out the wildcard object itself, which may or may not be what you want.
Mike