dm btree spine: remove extra node_check function declaration

Should have been removed as part of commit f73e2e70ec48 ("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>
1 file changed