hooks: eliminate post-update hook

hooks: eliminate post-update hook

The post-receive hook superseded the post-update hook some time
ago and since it receives its arguments on stdin instead of as
command line arguments, it cannot fail due to too many refs being
updated at once (and the command line length limit exceeded).

Move the prior post-update activies into post-receive and get
rid of post-update.

While we are in there we also stop calling `git update-server-info`
since we now set receive.updateserverinfo (v1.6.5.3 or later and
we now require v1.6.6 or later).

We also now always read all the refs even if there's no socket to
send them to so that git does not receive SIGPIPE if there's too
many of them.  The latest versions of Git handle the broken pipe
okay, but we support older versions so we must read all the refs
whether we're planning on doing anything with the info or not.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>