binfmt: remove taso from linux_binprm struct

With commit 987f20a9 ("a.out: Remove the a.out implementation"), the
use of the special taso flag for alpha architectures in the linux_binprm
struct is gone.

Remove the definition of taso in the linux_binprm struct.

No functional change.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220929203903.9475-1-lukas.bulwahn@gmail.com