Drop Unity 2019 support

[enitimeago]

Modular Avatar is planning to end support for Unity 2019 when the VRChat SDK moves from 2022.3.6f1 to 2022.3.22f1 due to availability of new features and the increasing difficulty of simultaneously supporting Unity 2019.

I'd like to also drop support for Unity 2019 in Make It MMD around the same time. This is for similar reasons, that is, to adopt new features as well as reduce my burden supporting multiple versions of Unity.

Further reading:

• Modular Avatar announcement (Japanese) https://twitter.com/bd_j/status/1785476789726515554