upload-pack: simplify request validation

upload-pack: simplify request validation

Long time ago, we used to punt on a large (read: asking for more
than 256 refs) fetch request and instead sent a full pack, because
we couldn't fit many refs on the command line of rev-list we run
internally to enumerate the objects to be sent.  To fix this,
565ebbf (upload-pack: tighten request validation., 2005-10-24),
added a check to count the number of refs in the request and matched
with the number of refs we advertised, and changed the invocation of
rev-list to pass "--all" to it, still keeping us under the command
line argument limit.

However, these days we feed the list of objects requested and the
list of objects the other end is known to have via standard input,
so there is no longer a valid reason to special case a full clone
request.  Remove the code associated with "create_full_pack" to
simplify the logic.

Signed-off-by: Junio C Hamano <gitster@pobox.com>