cogl/pango: Drop PANGO_ENABLE_BACKEND usage

Dropped before Pango 1.46 which is the min required version
so the backward compatibility is no longer needed

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3491>

clutter/clutter/clutter-settings.c

@@ -21,7 +21,6 @@
 
 #ifdef HAVE_PANGO_FT2
 /* for pango_fc_font_map_cache_clear() */
-#define PANGO_ENABLE_BACKEND
 #include <pango/pangofc-fontmap.h>
 #endif /* HAVE_PANGO_FT2 */
 

cogl/cogl-pango/cogl-pango-fontmap.c

@@ -28,12 +28,6 @@
 
 #include "config.h"
 
-/* This is needed to get the Pango headers to export stuff needed to
-   subclass */
-#ifndef PANGO_ENABLE_BACKEND
-#define PANGO_ENABLE_BACKEND 1
-#endif
-
 #include <pango/pango-fontmap.h>
 #include <pango/pangocairo.h>
 #include <pango/pango-renderer.h>

cogl/cogl-pango/cogl-pango-render.c

@@ -35,17 +35,6 @@
 
 #include "config.h"
 
-#ifndef PANGO_ENABLE_BACKEND
-#define PANGO_ENABLE_BACKEND 1
-#endif
-
-#ifndef PANGO_UNKNOWN_GLYPH_WIDTH
-#define PANGO_UNKNOWN_GLYPH_WIDTH 10
-#endif
-#ifndef PANGO_UNKNOWN_GLYPH_HEIGHT
-#define PANGO_UNKNOWN_GLYPH_HEIGHT 14
-#endif
-
 #include <pango/pango-fontmap.h>
 #include <pango/pangocairo.h>
 #include <pango/pango-renderer.h>
@@ -59,6 +48,9 @@
 #include "cogl-pango/cogl-pango-glyph-cache.h"
 #include "cogl-pango/cogl-pango-display-list.h"
 
+#define PANGO_UNKNOWN_GLYPH_WIDTH 10
+#define PANGO_UNKNOWN_GLYPH_HEIGHT 14
+
 enum
 {
   PROP_0,