Drop aarch64 platform subdir

Since veyron is gone, all devices we have now are theoretically
capable of running a 64-bit userspace.  Drop the allow-list of devices
that can.

BUG=none
TEST=compiles

Change-Id: I88db3958dd509bf7705f190c724309ae755307de
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/mosys/+/3508473
Tested-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-by: Jacob Rasmussen <jacobraz@google.com>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
6 files changed