fixed scope reference error when modal.remove() is called

When calling remove on a modal, I was noticing the following error in chrome.

ReferenceError: scope is not defined
    at http://localhost/lib/js/ionic/ionic-angular.js:227:9
    at http://localhost/lib/js/ionic/angular.js:13392:28
    at completeOutstandingRequest (http://localhost/lib/js/ionic/angular.js:4032:10)
    at http://localhost/lib/js/ionic/angular.js:4338:7 

This change assigns this to a self variable and uses the reference in the animate leave callback.