block: Drop unmaintained 'archipelago' driver

block: Drop unmaintained 'archipelago' driver

The driver has failed to build since commit da34e65, in qemu 2.6,
due to a missing include of qapi/error.h for error_setg().
Since no one has complained in three releases, it is easier to
remove the dead code than to keep it around, especially since it
is not being built by default and therefore prone to bitrot.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>