Fix test.sh on freebsd

Fix test.sh on freebsd

It turns out that in all conformant shells, "unset FOO" removes FOO
both from the shell's variables and from the exported environment.
(I've tested this on msys, opensolaris, linux, osx, and freebsd.)

And in nearly every shell I can find, "unset FOO; export FOO" does
the same as unset FOO... except in my FreeBSD VM, where the "export
FOO" sets the exported value of FOO equal to "".  This broke test.sh
for us.

The fix is simple: remove the needless exports!