Fix #456 issue of SCIPU in YUV444 format
Disable SCIPU (JVET-O0050) in YUV444 format. The problem of small blocks (2x4, 4x2, 2x2) stated in the proposal don't exist in YUV444 format. In addition, the function has conflicts with palette mode predictor.
Edited by Yung-Hsuan Chao (Jessie)