sh: Remove EXP_REDIR.

EXP_REDIR was supposed to generate pathnames in redirection if exactly one
file matches, as permitted but not required by POSIX in interactive mode. It
is unlikely this will be implemented.

No functional change is intended.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276037 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f