Revert "Fix crash when removing Routes and VCA"

There is probably a good reason why _vca.reset() is called
immediately, and 6dc66ea78f is a better solution to the issue

This reverts commit 83719fba1a.

gtk2_ardour/vca_time_axis.cc

@@ -129,6 +129,8 @@ VCATimeAxisView::~VCATimeAxisView ()
 void
 VCATimeAxisView::self_delete ()
 {
+	/* reset reference immediately rather than deferring to idle */
+	_vca.reset ();
 	delete_when_idle (this);
 }