Changes to ext-tx probs
Changes to ext-tx probs

Slight improvement in performance.
derflr: +1.828%

Change-Id: I74f5d3743a2b9c27e8b97c266c702dd1a791f73e

luctrudeau/aom,smarter/aom,GrokImageCompression/aom,smarter/aom,mbebenita/aom,smarter/aom,luctrudeau/aom,luctrudeau/aom,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,luctrudeau/aom,smarter/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,GrokImageCompression/aom,luctrudeau/aom,mbebenita/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,GrokImageCompression/aom,smarter/aom,GrokImageCompression/aom,smarter/aom