Fix -e option in contrib/intarray/bench/bench.pl.

As implemented, -e ran an EXPLAIN but then discarded the output, which
certainly seems pointless.  Make it print to stdout instead.  It's been
like that forever, so back-patch to all supported branches.

Daniel Gustafsson, reviewed by Andreas Scherbaum

Patch: <B97BDCB7-A3B3-4734-90B5-EDD586941629@yesql.se>