dm btree spine: remove extra node_check function declaration

Should have been removed as part of commit f73e2e70 ("dm btree
spine: remove paranoid node_check call in node_prep_for_write()")
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/persistent-data/dm-btree-spine.c

@@ -15,10 +15,6 @@
 
 #define BTREE_CSUM_XOR 121107
 
-static int node_check(struct dm_block_validator *v,
-		      struct dm_block *b,
-		      size_t block_size);
-
 static void node_prepare_for_write(struct dm_block_validator *v,
 				   struct dm_block *b,
 				   size_t block_size)