remote: use remote_state parameter internally

remote: use remote_state parameter internally

Without changing external-facing functions, replace
the_repository->remote_state internally by adding a struct remote_state
parameter.

As a result, external-facing functions are still tied to the_repository,
but most static functions no longer reference
the_repository->remote_state. The exceptions are those that are used in
a way that depends on external-facing functions e.g. the callbacks to
remote_get_1().

Signed-off-by: Glen Choo <chooglen@google.com>
Reviewed-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>