configure.ac: drop unused HAVE_BIN_SH

Summary:
This hugs heritage gone away with commit f1dffa0224c9e8dcf1d3908e888e7d683485791b
in 2001

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: tried to find HAVE_BIN_SH in internet, no success

Reviewers: simonmar, austin

Reviewed By: austin

Subscribers: phaskell, simonmar, relrod, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D117