JVET-P0621: HMVP cleaning
During JVET-P0621 discussion, it was agreed that the HMVP source code has to be cleaned so that only one motion information comparison function is used in the codec, the "==" operator (xCheckSimilarMotion has to be removed). The proposed merge request also removes some unnecessary parameters and defines a HMVP list update function to avoid divergences between encoder and decoder. It has been tested and results remain unchanged.