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_macros/src/lib.rs

@@ -6,8 +6,6 @@
 #![feature(proc_macro_span)]
 #![feature(proc_macro_tracked_env)]
 #![allow(rustc::default_hash_types)]
-#![deny(rustc::untranslatable_diagnostic)]
-#![deny(rustc::diagnostic_outside_of_impl)]
 #![allow(internal_features)]
 
 use synstructure::decl_derive;