chore(modal): Remove unused code

[wallin]

Just went through the modal code and noticed that there was an unused function. Not sure if it was left there intentionally for later use or just a leftover from the past

[pkozlowski-opensource]

@wallin Thnx so much for spotting this one, good catch! In fact we are in the process of refactoring (or more harmonizing) implementation of the modal and the $dialog service - you can see WIP in https://github.com/angular-ui/bootstrap/tree/refact/dialogmodal and more discussion in #128

So in the very near feature this unnecessary code will go away. Going to close this PR as getting it in would mean more difficult merge of the refactoring branch, but once again, thnx for looking into this and taking time opening this PR.

[wallin]

Sure! No problem. Keep up the good work!