Revert "Add Contributing.md with a set of label descriptions."

[SergeyTeplyakov]

Have no idea why Roslyn-based changes where applied with this pull request as well. Reverting it back.

Reverts #68

[sharwell]

@SergeyTeplyakov

1. This occurred for the same reason Add some missing system contracts; fix bad contracts in Application and ... #21 had issues. Pull request Add Contributing.md with a set of label descriptions. #68 was sent from your master branch, so when you later updated your master branch the new commits were automatically appended to the pull request. I included additional information about this scenario in Pull requests policies #62.
2. I think it would make sense to force-push to the master branch here to revert Add Contributing.md with a set of label descriptions. #68 by completely removing the commit from history. This is something we want to avoid in the future, but little (if any) work has been created on top of the current master branch and the repository currently contains new binary files which will never be used.

[SergeyTeplyakov]

Yep, I know why this happens. I'm using different local branches for different features right now.

I thought about force-push, but decided that this could do more harm than benefits...