Instructions
Launch "The Sims 3" game and load your saved game.
Press and hold the "Control," "Shift" and "C" buttons to activate the cheat text box.
Enter the cheat code "deleteallcharacters" into the text box in the top-right corner of the screen. A confirmation message will appear asking if you are sure you want to apply the cheat. Click the "Yes" button to activate the cheat.
Save and exit your game to apply the new cheat. Launch your saved game file and all the "townies" should be cleared from your Sims neighborhood.