Fixes some rd-debug mismatches coding cat6 tokens with tx size < 32x32.
For these tokens the high extrabits are elided during tokenization and
detokenization, but the rd cost was computed with the old tables from
VP9 where these high extrabits are always coded.

Change-Id: I4a9a6ea822ff821e1932c351d43a57bdb4d6d466