We should remove/deprecate `hadrian -c`

I don't think it's pulling it's weight.

• I saw people try to use it on #ghc and it going wrong repeatedly. Resulting in collective hours of lost time.
• It seems to currently be broken.
• It's not used on CI.
• Does it even properly work with nix?

I get that we want to make hadrian convenient. But as a maintainer it seems the costs add up to far much than the potential benefit.