[rustdoc] partially fix invalid files creation
Part of #111249. It only removes generation for modules which shouldn't exist. For files, we need the compiler to keep re-export information alive for external items so we can actually have the right path to their location as it's currently not generating them correctly.
In case the item is inlined, it shouldn't (and neither should its children) get a file generated.
r? ```@notriddle```
e100df9e68