With the preceding refactorings the `struct read_object_fd_data` is now
somewhat misnamed, as it doesn't only contain the data anymore, but also
the stream itself. Rename the structure to `struct fd_stream` to better
match the new structure.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>