add missing define in config.h.in

include/assimp/config.h.in

@@ -657,7 +657,11 @@ enum aiComponent
 */
 #define AI_CONFIG_IMPORT_FBX_EMBEDDED_TEXTURES_LEGACY_NAMING \
 	"AI_CONFIG_IMPORT_FBX_EMBEDDED_TEXTURES_LEGACY_NAMING"
-	
+
+// ---------------------------------------------------------------------------
+#define AI_CONFIG_IMPORT_REMOVE_EMPTY_BONES \
+    "AI_CONFIG_IMPORT_REMOVE_EMPTY_BONES"
+
 // ---------------------------------------------------------------------------
 /** @brief  Set the vertex animation keyframe to be imported
  *