Refactor transform selection process
Refactor transform selection process

This commit re-arranges the transform type and size selectio
process. It removes an unnecessary rate-distortion cost computation
step. Local experiments show that this speeds up the encoding
process by 6% for both the baseline and the ext-intra experiment.

Change-Id: Iab3b86a63a1e9e55548466791ed5d29a0575c1e7

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