builtin-remote: rename variables and eliminate redundant function call

builtin-remote: rename variables and eliminate redundant function call

- The variable name "remote" is used as both a "char *" and as a "struct
  remote *"; this is confusing, so rename the former to remote_name.

- Consistently refer to the refs returned by transport_get_remote_refs()
  as remote_refs.

- There is no need to call "sort_string_list(&branch_list)" as
  branch_list is populated via string_list_insert(), which maintains its
  order.

Signed-off-by: Jay Soffian <jaysoffian@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>