Remove build artifacts from the repository

[cmahnke]

Keeping old build artifacts inside of the repository is considered bad practise:

• It blows up the repository with redundant (they should be completely recreateable by building them) files
• It slows down cloning considerably (I'm currently on a train and don't want outdated files)

Please remove the complete Builds directory. Even better would be a filtering the repo and force push it again to rid the history of those files as well.

Consider using GitHub Actions to build artifacts for multiple operating systems.

[cmahnke]

Also add the Unity logs to .gitignore