Remove deprecated no-op function (2/2)

Glib::thread_init has been deprecated since 2.32,ib
is no longer necessary and no longer has any effect.

This fixes builds with modern glib[mm] versions, notably
with msys2 in Windows.

gtk2_ardour/canvas_test.cc

@@ -262,10 +262,6 @@ int main (int argc, char **argv)
 		::exit (EXIT_FAILURE);
 	}
 
-	if (!Glib::thread_supported()) {
-		Glib::thread_init();
-	}
-
 	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
 
 	log_receiver.listen_to (info);

gtk2_ardour/main.cc

@@ -261,10 +261,6 @@ int main (int argc, char *argv[])
 
 	load_custom_fonts(); /* needs to happen before any gtk and pango init calls */
 
-	if (!Glib::thread_supported()) {
-		Glib::thread_init();
-	}
-
 #ifdef LXVST_SUPPORT
 	XInitThreads ();
 #endif

gtk2_ardour/toolbar_test.cc

@@ -272,10 +272,6 @@ int main (int argc, char **argv)
 		::exit (EXIT_FAILURE);
 	}
 
-	if (!Glib::thread_supported()) {
-		Glib::thread_init();
-	}
-
 	pthread_setcanceltype (PTHREAD_CANCEL_ASYNCHRONOUS, 0);
 
 	log_receiver.listen_to (info);