protocol-caps.c: fix memory leak in send_info()

protocol-caps.c: fix memory leak in send_info()

Fix a memory leak in a2ba162cda (object-info: support for retrieving
object info, 2021-04-20) which appears to have been based on a
misunderstanding of how the pkt-line.c API works. There is no need to
strdup() input to packet_writer_write(), it's just a printf()-like
format function.

This fixes a potentially large memory leak, since the number of OID
lines the "object-info" call can be arbitrarily large (or a small one
if the request is small).

This makes t5701-git-serve.sh pass again under SANITIZE=leak, as it
did before a2ba162cda2.

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