Unload module from GHC session after a source file is renamed/moved/deleted

Steps to repro:

1. Create a project with two modules:
```
module Numeric where
-- shadows the Numeric module in base
```
```
module A where
import Numeric (showInt) -- error: Numeric doesn't export showInt
```
2. Delete the `Numeric` module
3. `A` still refuses to typecheck as it doesn't see the real `Numeric` module