fix(gs/achilles): Get rid of universalization step

The step of "universalizing" function expressions was conflicting with
top-level ascriptions for polymorphic function declarations:
universalization generates universal type variables, and top-level
polymorphic ascription *also* generates universal type variables, and
the two were conflicting with each other when unifying. Let's just get
rid of this now, and we can bring it back in a more principled manner
once we do actual let-generalization (which there's still an ignored
test case for)

Change-Id: Idc08c8cb5ac92d1e6e1e63c9b8729176cab73f44
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2616
Tested-by: BuildkiteCI
Reviewed-by: glittershark <grfn@gws.fyi>

users/glittershark/achilles/src/ast/hir.rs

@@ -228,6 +228,13 @@ pub enum Decl<'a, T> {
 }
 
 impl<'a, T> Decl<'a, T> {
+    pub fn name(&self) -> &Ident<'a> {
+        match self {
+            Decl::Fun { name, .. } => name,
+            Decl::Extern { name, .. } => name,
+        }
+    }
+
     pub fn type_(&self) -> Option<&T> {
         match self {
             Decl::Fun { type_, .. } => Some(type_),