Cleanup: remove unused node type

This wasn't used for backwards compatibility, because Blender does not
read from the `nodetype` anywhere. It also wasn't used for forward
compatibility, because it was not initialized for new node groups.

source/blender/blenloader/intern/versioning_250.c

@@ -2272,18 +2272,6 @@ void blo_do_versions_250(FileData *fd, Library *lib, Main *bmain)
       }
       FOREACH_NODETREE_END;
     }
-
-    {
-      /* Initialize group tree nodetypes.
-       * These are used to distinguish tree types and
-       * associate them with specific node types for polling.
-       */
-      bNodeTree *ntree;
-      /* all node trees in bmain->nodetree are considered groups */
-      for (ntree = bmain->nodetrees.first; ntree; ntree = ntree->id.next) {
-        ntree->nodetype = NODE_GROUP;
-      }
-    }
   }
 
   if (!MAIN_VERSION_ATLEAST(bmain, 259, 4)) {

source/blender/makesdna/DNA_node_types.h

@@ -511,11 +511,6 @@ typedef struct bNodeTree {
   int cur_index;
   int flag;
 
-  char _pad1[4];
-
-  /** Specific node type this tree is used for. */
-  int nodetype DNA_DEPRECATED;
-
   /** Quality setting when editing. */
   short edit_quality;
   /** Quality setting when rendering. */