Remove the long-deprecated -u option from psql, since it does nothing very

Remove the long-deprecated -u option from psql, since it does nothing very
useful and confuses people who think it is the same as -U.  (Eventually
we might want to re-introduce it as being an alias for -U, but that should
not happen until the switch has actually not been there for a few releases.)
Likewise in pg_dump and pg_restore.  Per gripe from Robert Treat and
subsequent discussion.