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_expand/src/base.rs

@@ -1,5 +1,3 @@
-#![deny(rustc::untranslatable_diagnostic)]
-
 use crate::base::ast::NestedMetaItem;
 use crate::errors;
 use crate::expand::{self, AstFragment, Invocation};