Fix orientationchange disable property documentation

The documentation states that for the `orientationchange` event to only use size comparisons without listening for browser-generated orientationchange events, one has to set the `$.mobile.orientationChangeEnabled` to `false`. The problem is that the current implementation for this event only checks for `$.event.special.orientationchange.disabled` property. There is an actual reference in code to  `$.mobile.orientationChangeEnabled` but it is not used anywhere and seems to be obsolete. The `orientationchange.disabled` property is assumed to be boolean but its semantics are the other way around compared to the `orientationChangeEnabled` property. This means that to not use browser-generated orientationchange events, one has to set this property to `true`. The default value for this property is not defined, this will evaluate to `false` in code by default which enables listening to browser-generated orientationchange events.

This pull request fixes the documentation to describe the property the code actually listens to instead of the dead one.