Compatibility fix for 'ln -sf'.

ln of Solaris 8 only accepts "ln -f -s" (in that order), but as the -f isn't
needed here, I simply dropped it.

tests/test-symlinks

@@ -35,7 +35,7 b' rm a.c'
 rm dir/a.o
 rm dir/b.o
 mkdir dir/a.o
-ln -sf nonexist dir/b.o
+ln -s nonexist dir/b.o
 mkfifo a.c
 # it should show a.c, dir/a.o and dir/b.o deleted
 hg status