lambda: [CHANGES OUTPUT] Change the distortion weights applied to chroma.

Inside R-D, a single lambda is applied for both luma and chroma. To account for the different QPs,
(as defined by the standard) the chroma distortion was weighted by a factor proportional to the
difference in QPs. This patch eliminates the extra weighting given to the chroma distortion
(since it is visually less perceptible).
x265_encoder_encode: don't return 0 while flushing.
encoder: cleanup obsolete NAL data fields
encoder: remove redundant flush argument