build: Use workspace global lints

In relatively recent rust there's a nice way to globally
configure clippy lints for the whole workspace. We can
kill the `custom-lints` target because relatively
recently clippy has a lint for `todo!` and `dbg!` itself.

Signed-off-by: Colin Walters <walters@verbum.org>

.github/workflows/ci.yml

@@ -41,8 +41,6 @@ jobs:
         run: cd lib && cargo check --no-default-features
       - name: Individual checks
         run: (cd cli && cargo check) && (cd lib && cargo check)
-      - name: Lints
-        run: cargo xtask custom-lints
       - name: Run tests
         run: cargo test -- --nocapture --quiet
       - name: Manpage generation