ty: simplify transparent_newtype_field

This commit removes the normalization from `transparent_newtype_field` -
turns out it wasn't necessary and that makes it a bunch simpler -
particularly when handling projections.

Signed-off-by: David Wood <david@davidtw.co>

src/test/ui/lint/lint-ctypes-73249-4.rs

@@ -0,0 +1,24 @@
+// check-pass
+#![deny(improper_ctypes)]
+
+use std::marker::PhantomData;
+
+trait Foo {
+    type Assoc;
+}
+
+impl Foo for () {
+    type Assoc = PhantomData<()>;
+}
+
+#[repr(transparent)]
+struct Wow<T> where T: Foo<Assoc = PhantomData<T>> {
+    x: <T as Foo>::Assoc,
+    v: u32,
+}
+
+extern "C" {
+    fn test(v: Wow<()>);
+}
+
+fn main() {}