upload-pack: remove packet debugging harness
If you set the GIT_DEBUG_SEND_PACK environment variable,
upload-pack will dump lines it receives in the receive_needs
phase to a descriptor. This debugging harness is a strict
subset of what GIT_TRACE_PACKET can do. Let's just drop it
in favor of that.
A few tests used GIT_DEBUG_SEND_PACK to confirm which
objects get sent; we have to adapt them to the new output
format.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>