Remove -i/--ignore-version option from pg_dump, pg_dumpall and pg_restore.

Remove -i/--ignore-version option from pg_dump, pg_dumpall and pg_restore.

The commit c22ed3d523782c43836c163c16fa5a7bb3912826 turned
the -i/--ignore-version options into no-ops and marked as deprecated.
Considering we shipped that in 8.4, it's time to remove all trace of
those switches, per discussion. We'd still have to wait a couple releases
before it'd be safe to use -i for something else, but it'd be a start.