We no longer use these in any of our images. Clean-up the remaining
comments and documentation that reference them and remove from the
build.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220914155950.804707-31-alex.bennee@linaro.org>