[oe] libvpx should not inherit autotools

[Khem Raj]

Hi Koen

libvpx recipes are inheriting autotools while it seems to me that they
should not. Yes it does have a configure script but its not autoconf
generated but a hand written one
and there are no other traces of autoconf or automake and stuff that
goes with normal automake autoconf build systems.

Would you take a look at it ?

Thanks
-Khem