Doc: Removing url variable from qdocconf file.

-url inherited from the url variable set in qtbase/doc/global

Change-Id: I8a417699e2b2e7a33a3b4a3ccc6174e99955ebbe
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Martin Smith <martin.smith@digia.com>