Change pg_listener attribute number constants to match the usual pattern

It appears that, for no particularly good reason, pg_listener.h deviates from
the usual convention for declaring attribute number constants.  Normally, it's

#define Anum_{catalog-name}_{column-name}  {attribute-number}

pg_listener.h, however substitutes a different string that is similar, but not
the same as, the column name.  This change fixes that.

Author: Robert Haas <robertmhaas@gmail.com>