To remove a listing from StreetEasy, simply navigate to the listing in your Company Listings tab. From there, click on the listing to open and uncheck the Syndicate to StreetEasy checkbox (found in the marketing section of the listing):
Please Note: Removing a listing from StreetEasy will also remove the listing from Zillow, Trulia and HotPads. Your listing will still be syndicated to the remaining sites you're set up to post on.
For full details on how you manage your listings sent to StreetEasy, check out the article Managing StreetEasy: How to Add and Remove Listings and Agents.