When we initialize the hashmap, we give it a pointer to the
diff_options, which it then passes along to each call of the
hashmap_cmp_fn function. There's no need to pass it a second time as
the "keydata" parameter, and our comparison functions never look at
keydata.

This was a mistake left over from an earlier round of 2e2d5ac1
(diff.c: color moved lines differently, 2017-06-30), before hashmap
learned to pass the data pointer for us.
Explanation-by: NJeff King <peff@peff.net>
Signed-off-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>