Remove SystemUIDialog subclass from InternetDialog

Renames InternetDialogFactory to InternetDialogManager since its real
responsibility is to manager the existence of a single dialog at a
time rather than create dialogs.

This code needs more tlc in the future, but that is beyond the scope
of the current bug.

Flag: NA
Bug: 219008720
Test: build and run internet dialog
Change-Id: If1bdfabdab99aa34641fe37824de7e80f68160bc