erlang: remove non-SMP build option

The non-SMP scheduler was deprecated with the Erlang/OTP 20.0 release and
slated for removal with the next major Erlang release. Since the non-SMP
scheduler isn't even built anymore, this option no longer has the
intended effect of saving space or compile time. The SMP scheduler
supports both SMP and non-SMP processors, so removing the option will
not break any platforms.

We do not need to add a legacy entry, because the new behavior is the
same as with the option previously set (i.e. SMP enabled).

Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>