bpf: Remove unused MT_ENTRY define

The range tree introduction removed the need for maple tree usage
but missed removing the MT_ENTRY defined value that was used to
mark maple tree allocated entries.

Remove the MT_ENTRY define.

Fixes: b795379 ("bpf: Introduce range_tree data structure and use it in bpf arena")
Signed-off-by: Lorenzo Pieralisi <[email protected]>
Cc: Andrii Nakryiko <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Daniel Borkmann <[email protected]>

kernel/bpf/arena.c

@@ -257,8 +257,6 @@ static void arena_vm_close(struct vm_area_struct *vma)
 	kfree(vml);
 }
 
-#define MT_ENTRY ((void *)&arena_map_ops) /* unused. has to be valid pointer */
-
 static vm_fault_t arena_vm_fault(struct vm_fault *vmf)
 {
 	struct bpf_map *map = vmf->vma->vm_file->private_data;