Implicitly infer the number of MMVD base merge candidate to be 1 as MaxNumMergeCand being equal to 1, and mmvd_merge_flag is not signalled in this case.

- tiles are in the VVC spec for 3 meeting cycles now
- cleanup helps with adaptation for tiles to current draft

VTM version 4.2

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.