Move lints list to .carg/config.toml (#1394)

That way they apply to all crates equally.

See https://github.com/EmbarkStudios/rust-ecosystem/issues/22 for why.

egui_demo_app/src/lib.rs

@@ -1,8 +1,3 @@
-// Forbid warnings in release builds:
-#![cfg_attr(not(debug_assertions), deny(warnings))]
-#![forbid(unsafe_code)]
-#![warn(clippy::all, rust_2018_idioms)]
-
 #[cfg(target_arch = "wasm32")]
 use eframe::wasm_bindgen::{self, prelude::*};