x11: Drop unused function

The meta_prop_get_motif_hints() function was only used in the
old MetaUI frames code. The remaining code in mutter accesses
directly the MetaPropValue when loading properties for a window,
and does not use this API call.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2741>

src/x11/xprops.c

@@ -318,23 +318,6 @@ motif_hints_from_results (GetPropertyResults *results,
   return TRUE;
 }
 
-gboolean
-meta_prop_get_motif_hints (MetaX11Display *x11_display,
-                           Window          xwindow,
-                           Atom            xatom,
-                           MotifWmHints  **hints_p)
-{
-  GetPropertyResults results;
-
-  *hints_p = NULL;
-
-  if (!get_property (x11_display, xwindow, xatom, AnyPropertyType,
-                     &results))
-    return FALSE;
-
-  return motif_hints_from_results (&results, hints_p);
-}
-
 static gboolean
 latin1_string_from_results (GetPropertyResults *results,
                             char              **str_p)

src/x11/xprops.h

@@ -69,10 +69,6 @@ typedef struct {
 /* These all return the memory from Xlib, so require an XFree()
  * when they return TRUE. They return TRUE on success.
  */
-gboolean meta_prop_get_motif_hints   (MetaX11Display *x11_display,
-                                      Window          xwindow,
-                                      Atom            xatom,
-                                      MotifWmHints  **hints_p);
 gboolean meta_prop_get_cardinal_list (MetaX11Display *x11_display,
                                       Window          xwindow,
                                       Atom            xatom,