aes: Remove unused code (NDEBUG, u16)

aes: Remove unused code (NDEBUG, u16)

The current code includes assert.h very early (from qemu-common.h),
so the definition of NDEBUG was without any effect.

In the initial version from 2004, NDEBUG was used to disable the assertions.
Those assertions are not in time critical code, so it is no longer
reasonable to disable them and the definition of NDEBUG can be removed.

Type u16 is also unused and therefore does not need a type definition.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>