MMVD simplification by removing the two largest distance entries in the
MMVD distance table using encoder only change method.
To make the number of MMVD distance entries configurable by the
software, additionally adding 'MmvdDisNum' as a new option in the cfg files.

Code was salvaged from !306

When MC for luma only is desired, use existing luma/chroma parameters
instead of encoder-specific field in data structure

Also take care that luma only MC doesn't imply IBC

Deleted the TU retrieval from the DQP code in xCompressCU and the TU pointer being equal to nullptr check.

Dereferencing a nullptr should be avoided, even if the passed object is never used.
It may not be the most elegant solution to pass an empty list object, but it should work.