main: Move grab op macro to relevant file

It was in main-private.h for some reason, but only used in display.c.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1833>

src/core/display.c

@@ -173,6 +173,8 @@ enum
 
 static guint display_signals [LAST_SIGNAL] = { 0 };
 
+#define META_GRAB_OP_GET_BASE_TYPE(op) (op & 0x00FF)
+
 /*
  * The display we're managing.  This is a singleton object.  (Historically,
  * this was a list of displays, but there was never any way to add more

src/core/main-private.h

@@ -37,8 +37,6 @@ typedef enum _MetaX11DisplayPolicy
   META_X11_DISPLAY_POLICY_DISABLED,
 } MetaX11DisplayPolicy;
 
-#define META_GRAB_OP_GET_BASE_TYPE(op) (op & 0x00FF)
-
 META_EXPORT_TEST
 void meta_override_compositor_configuration (MetaCompositorType compositor_type,
                                              GType              backend_gtype,