mw.ViewPageTarget.init: Simplify hideLoading and pushState

Follows-up Ica33de675, If505a46f54.

* The setting of 'uri' looked like a redundant local alias before
  passing on to pushState, but is actually important on itself.

* Remove binding for hideLoading. It's a detachable method on
  a singleton, not an instance method.

Change-Id: Ic3536caf3f42ee893124312fd5981b67336bd480