Fixes cancel button error on Action Sheet

The fix that was supposed to close this doesn't:

https://github.com/driftyco/ionic/commit/ba39fb0046cf9ff8b3d18fb8ac7d10d734afe192

The real problem was that cancel was being called on opts and not on scope. The code by @ajoslin is redundant as all the three functions he gives a default angular.noop are overloaded 20 lines below so I reverted it.