Eliminate the big superblock row buffer.
Eliminate the big superblock row buffer.

Now only buffering three lines across the entire frame and four lines
over the height of one superblock.

No change in output.

Change-Id: I6b99399974e197dc02f2e4ff2e60cdd7fdaa2e43

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