Remove config.sub

It's annoying to work with it as GHC configure is constantly modifying it. Why generated file is commited?

```
error: Your local changes to the following files would be overwritten by checkout:
	config.sub
Please commit your changes or stash them before you switch branches.
Aborting
fatal: Unable to checkout '3be0223cee7395410915a127eba3acae5ff0b2f2' in submodule path 'libraries/unix'
```