Makefile.inc1: garbage collect unused variable: install-info

The variable's definition was removed with texinfo in
2d28136, but the reference to the
variable was left behind.

This is effectively a no-op cleanup.

MFC after:	3 days

Author: ngie-eign

Makefile.inc1

@@ -1417,7 +1417,7 @@ _sysctl=sysctl
 .endif
 
 ITOOLS=	[ awk cap_mkdb cat chflags chmod chown cmp cp \
-	date echo egrep find grep id install ${_install-info} \
+	date echo egrep find grep id install \
 	ln make mkdir mtree mv pwd_mkdb \
 	rm sed services_mkdb sh sort strip ${_sysctl} test time true uname wc