chroot_version_hooks.d: drop support for upgrading SDKs pre-2021

Punt old upgrade hooks that only get used for SDKs that were created
before 2021 and have not been upgraded since.  The tooling will already
detect this scenario (because the upgrade hooks are missing) and throw
an error telling the user to recreate the SDK.

BUG=None
TEST=CQ passes

Change-Id: I3d6a7e72ab8d04cd44b79e9356a0833d8545d56a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosutils/+/3621320
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Ram Chandrasekar <rchandrasekar@google.com>
Commit-Queue: Ram Chandrasekar <rchandrasekar@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
21 files changed