Rollup merge of #69920 - Centril:hir-cleanup, r=Zoxc

Rollup merge of #69920 - Centril:hir-cleanup, r=Zoxc

Remove some imports to the rustc crate

- When we have `NestedVisitorMap::None`, we use `type Map = dyn intravisit::Map<'v>;` instead of the actual map. This doesn't actually result in dynamic dispatch (in the future we may want to use an associated type default to simplify the code).

- Use `rustc_session::` imports instead of `rustc::{session, lint}`.

r? @Zoxc