Remove wxWebRequestImpl::IsActiveState()

Semantics of this function wasn't really clear and it was used only
once, so just inline it at the point of use and define better what
happens for various states there.

Also use a switch rather than testing for individual states to make sure
this code is updated if another state is added in the future.

No real changes.

include/wx/private/webrequest.h

@@ -122,8 +122,6 @@ protected:
     // for the response status.
     void SetFinalStateFromStatus();
 
-    static bool IsActiveState(wxWebRequest::State state);
-
 private:
     // Called from public Cancel() at most once per object.
     virtual void DoCancel() = 0;