Invert diagnostic lints.

That is, change `diagnostic_outside_of_impl` and
`untranslatable_diagnostic` from `allow` to `deny`, because more than
half of the compiler has be converted to use translated diagnostics.

This commit removes more `deny` attributes than it adds `allow`
attributes, which proves that this change is warranted.

compiler/rustc_ast_lowering/src/lib.rs

@@ -35,8 +35,6 @@
 #![doc(rust_logo)]
 #![feature(box_patterns)]
 #![feature(let_chains)]
-#![deny(rustc::untranslatable_diagnostic)]
-#![deny(rustc::diagnostic_outside_of_impl)]
 
 #[macro_use]
 extern crate tracing;