Use EXECUTE FUNCTION syntax for triggers more

Use EXECUTE FUNCTION syntax for triggers more

Change pg_dump and ruleutils.c to use the FUNCTION keyword instead of
PROCEDURE in trigger and event trigger definitions.

This completes the pieces of the transition started in
0a63f996e018ac508c858e87fa39cc254a5db49f that were kept out of
PostgreSQL 11 because of the required catversion change.

Discussion: https://www.postgresql.org/message-id/381bef53-f7be-29c8-d977-948e389161d6@2ndquadrant.com