daala_tx: Remove +1/-1 butterflies from 4-point tx
daala_tx: Remove +1/-1 butterflies from 4-point tx

This fixes a potential overflow when using the 4-point Type VII DST
as the row transform in a 4x16 transform block.

Results on subset1:

https://arewecompressedyet.com/?job=%402017-12-03T01%3A27%3A43.842Z&job=%402017-12-03T01%3A27%3A43.842Z%402017-12-03T01%3A29%3A23.170Z

  PSNR | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.0113 |   0.0367 | 0.0063 |  0.0013 |     0.0182

Change-Id: Ib8ca6a2e06cd7d1b625cbbadcded2488eececd9c

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom