streaming.c: remove {open,close,read}_method_decl() macros

streaming.c: remove {open,close,read}_method_decl() macros

Remove the {open,close,read}_method_decl() macros added in
46bf043807c (streaming: a new API to read from the object store,
2011-05-11) in favor of inlining the definition of the arguments of
these functions.

Since we'll end up using them via the "{open,close,read}_istream_fn"
types we don't gain anything in the way of compiler checking by using
these macros, and as of preceding commits we no longer need to declare
these argument lists twice. So declaring them at a distance just
serves to make the code less readable.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>