Remove unused assignments

Remove unused assignments

These variables were always overwritten or the assigned
value was unused:

  builtin-diff-tree.c::cmd_diff_tree(): nr_sha1
  builtin-for-each-ref.c::opt_parse_sort(): sort_tail
  builtin-mailinfo.c::decode_header_bq(): in
  builtin-shortlog.c::insert_one_record(): len
  connect.c::git_connect(): path
  imap-send.c::v_issue_imap_cmd(): n
  pretty.c::pp_user_info(): filler
  remote::parse_refspec_internal(): llen

Signed-off-by: Benjamin Kramer <benny.kra@googlemail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>