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_infer/src/lib.rs

@@ -16,6 +16,8 @@
 #![doc(rust_logo)]
 #![feature(rustdoc_internals)]
 #![allow(internal_features)]
+#![allow(rustc::diagnostic_outside_of_impl)]
+#![allow(rustc::untranslatable_diagnostic)]
 #![feature(associated_type_bounds)]
 #![feature(box_patterns)]
 #![feature(extend_one)]