lrzsz: add lrz/lsz symlinks

Many systems support automatic zmodem transfers without needing to first
manually run the zmodem utils.  But the expectation is to run `lrz` and
not `rz`.  So install symlinks for lrz->rz and lsz->sz to support this.

This also includes a small fix to also remove sz when cleaning.

[Peter: use addprefix rather than patsubst]
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>