cogl-winsys: Remove the get_vsync_counter virtual

This function is only used internally within the GLX winsys so there
doesn't seem to be much point in it being a virtual winsys backend
function.

cogl/winsys/cogl-winsys-egl.c

@@ -1385,13 +1385,6 @@ _cogl_winsys_onscreen_set_visibility (CoglOnscreen *onscreen,
 }
 #endif
 
-static guint32
-_cogl_winsys_get_vsync_counter (void)
-{
-  /* Unsupported feature */
-  return 0;
-}
-
 static void
 _cogl_winsys_onscreen_swap_buffers (CoglOnscreen *onscreen)
 {
@@ -1510,7 +1503,6 @@ static CoglWinsysVtable _cogl_winsys_vtable =
       _cogl_winsys_onscreen_add_swap_buffers_callback,
     .onscreen_remove_swap_buffers_callback =
       _cogl_winsys_onscreen_remove_swap_buffers_callback,
-    .get_vsync_counter = _cogl_winsys_get_vsync_counter
   };
 
 /* XXX: we use a function because no doubt someone will complain

cogl/winsys/cogl-winsys-glx.c

@@ -1926,7 +1926,6 @@ static CoglWinsysVtable _cogl_winsys_vtable =
     .onscreen_remove_swap_buffers_callback =
       _cogl_winsys_onscreen_remove_swap_buffers_callback,
     .onscreen_set_visibility = _cogl_winsys_onscreen_set_visibility,
-    .get_vsync_counter = _cogl_winsys_get_vsync_counter,
 
     /* X11 tfp support... */
     /* XXX: instead of having a rather monolithic winsys vtable we could

cogl/winsys/cogl-winsys-private.h

@@ -123,9 +123,6 @@ typedef struct _CoglWinsysVtable
   (*onscreen_set_visibility) (CoglOnscreen *onscreen,
                               gboolean visibility);
 
-  guint32
-  (*get_vsync_counter) (void);
-
 #ifdef COGL_HAS_XLIB_SUPPORT
   gboolean
   (*texture_pixmap_x11_create) (CoglTexturePixmapX11 *tex_pixmap);