If you wish to remove all your mods and completely revert the game to an unmodded status for whatever reason and start from scratch, you'll have to install the game from scratch and also create a new save game. This should work for any Steam game.
If you wish to do so, follow these steps:
1. Start Steam. 2. Uninstall your game via Steam by right-clicking on the Game name in the Steam Games List and clicking Uninstall. 3. Exit Steam. 4. Delete all the files in the game directory (usually \Steam\steamapps\common\<GameName>) that may remain (those would likely belong to mods). 5. Start Steam.* 6. Reinstall the game via Steam and wait until everything is downloaded (Don't start the game when it's done!).* 7. Switch Steam to Offline Mode (Steam->Go offline), and wait for Steam to restart in Offline mode or disconnect your internet. 8. Exit Steam. 9. Delete your save game directory (usually \Steam\SteamApps\userdata\<YourSteamUserId>\<SteamGameId>). 10. Start Steam in Offline Mode. 11. Start the game. 12. Create a new save game. 13. Save the game (in WWE 2k Games, you can do so by changing an attribute or whatever of one of the Superstars and saving it). 14. Exit the game. 15. Start Steam in Online mode (you'll have to be connected to the Internet). 16. Start the Game. 17. If Steam tells you about a save conflict and which one to use, choose the one on your Computer and not the one in the Steam Cloud (this will update the save game in the cloud with the new, clean one). 18. Enjoy your clean, modless game.
* Note that you may be able to skip steps 5 and 6 if you have created backups of your clean game directory before modding and just copy your clean copy over instead.