Disable RDO of transform type for inter blocks
Disable RDO of transform type for inter blocks

After this change, transform type and size RDO is only performed
for intra blocks. In future, we should add speed settings to enable
a wider search at slower speed levels.

AWCY results at speed 5 show a 23% increase in encoding speed with mixed results in metrics:

speed-5-fine-dir@2020-05-09T12:44:38.812Z -> disable-inter-tx-type-rdo@2020-05-09T14:03:09.263Z

  PSNR | PSNR Cb | PSNR Cr | PSNR HVS |   SSIM | MS SSIM | CIEDE 2000
0.6422 | -0.8994 | -0.6326 |  -0.0105 | 0.1596 | -0.1235 |    -0.1157
xiph/rav1e,xiph/rav1e