Drop all references to git daily snapshots of Linux mainline git tree
since they are no longer generated.

Drop the "Last update" info since 'git log' is a better source of that
info and since the Last update date is not being updated.

Yes, I read that this file is obsolete, but it still has some useful
information in it.
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>