Use CallsManager in MainWindow and NewCallBox

This removes the status message at the end of the NewCallBox, since it
will be replaced by a permanent InfoBar.

As a side effect this removes also the disconnect message when a call
ends.
Fixes: https://source.puri.sm/Librem5/calls/issues/119

src/calls-new-call-box.h

@@ -25,8 +25,6 @@
 #ifndef CALLS_NEW_CALL_BOX_H__
 #define CALLS_NEW_CALL_BOX_H__
 
-#include "calls-provider.h"
-
 #include <gtk/gtk.h>
 
 G_BEGIN_DECLS
@@ -35,7 +33,7 @@ G_BEGIN_DECLS
 
 G_DECLARE_FINAL_TYPE (CallsNewCallBox, calls_new_call_box, CALLS, NEW_CALL_BOX, GtkBox);
 
-CallsNewCallBox * calls_new_call_box_new  (CallsProvider   *provider);
+CallsNewCallBox * calls_new_call_box_new  (void);
 void              calls_new_call_box_dial (CallsNewCallBox *self,
                                            const gchar     *target);