Unfortunately, at this time there is no way to delete Smart Matches from the list of all the suggested matches.
Thank you for your input.
We have received many requests for this feature from our users, and it is something that we are working on at this very moment. A new Smart Matching interface will be released in the very near future offering deletion, collaboration and many other enhancements. Please stay tuned, it's worth waiting for!
Note: if you are using the Family Tree Builder software, you can mark certain matches as confirmed if they are correct, or rejected if they are wrong. To do so, go to the Matches section in the program, and then click any person to see their matches. Select the relevant match or matches, and click on the "Change Status..." button at the top of the page.
Confirming or rejecting matches is recommended as a way to work your way through your Smart Matches and spot new ones that you have not yet handled easily.