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-main-window.h

@@ -27,7 +27,6 @@
 
 #include <gtk/gtk.h>
 
-#include "calls-provider.h"
 #include "calls-contacts.h"
 
 G_BEGIN_DECLS
@@ -37,7 +36,6 @@ G_BEGIN_DECLS
 G_DECLARE_FINAL_TYPE (CallsMainWindow, calls_main_window, CALLS, MAIN_WINDOW, GtkApplicationWindow);
 
 CallsMainWindow *calls_main_window_new  (GtkApplication  *application,
-                                         CallsProvider   *provider,
                                          GListModel      *record_store,
                                          CallsContacts   *contacts);
 void             calls_main_window_dial (CallsMainWindow *self,