Preventing webform saving in database
There is a module that's compatible with the 7.x-3.x branch that gives you the option to do just that:


  This module adds the ability to choose whether a webform should be saved to database or not. Within settings of each webform you can choose the option.


There is also a related issue in Webform's queue that is tracking the progress of getting the functionality into the webform module.

If you don't want to use the sandbox module, I'm sure you could check out the source and see what they're doing differently from what you have posted above.