Auto merge of #161043 - mejrs:rustc_session-lints, r=camelid

rustc_session; remove rustc_lint_defs re-exports



Some crates and tools were depending on just rustc_session for its re-exporting of an entire crate.

rustc_lint still re-exports rustc_lint_defs; that one would have been rather messy to remove because a lot of modules in clippy/rustdoc would have to import some from one and some from the other.