Fix CREATE EVENT TRIGGER syntax synopsis in documentation.

Dimitri Fontaine, per a report from Thom Brown
Fix a few small bugs in yesterday's event trigger patch.

Dimitri Fontaine
doc: Fix declared number of columns in table

This was broken in 841a5150c575ccd89e4b03aec66eeeefb21f3cbe.
pg_upgrade:  remove --single-transaction usage

With AtEOXact applied, --single-transaction makes pg_restore slower, and
has the potential to require lock table configuration, so remove the
argument.

Per suggestion from Tom.