Suppress bogus printout during new 035_standby_logical_decoding.pl test.

Our convention for some time has been that successful tests shouldn't
print anything on stderr.  A stray "diag" call violated that, and
for that matter messed up the normal TAP progress display.

Author: tglsfdc

src/test/recovery/t/035_standby_logical_decoding.pl

@@ -460,7 +460,7 @@ sub check_for_invalidation
 reactive_slots_change_hfs_and_wait_for_xmins('row_removal_', 'shared_row_removal_', 0, 1);
 
 # Trigger the conflict
-diag $node_primary->safe_psql('testdb', qq[
+$node_primary->safe_psql('testdb', qq[
   CREATE ROLE create_trash;
   DROP ROLE create_trash;
   VACUUM pg_authid;