Remove Sugar enum and inline single variant into CalledVia

compiler/module/src/called_via.rs

@@ -13,13 +13,8 @@ pub enum CalledVia {
     /// Calling with a unary operator, e.g. (!foo bar baz) or (-foo bar baz)
     UnaryOp(UnaryOp),
 
-    /// This call is the result of some desugaring, e.g. "\(first) \(last)" is
-    /// transformed into first ++ last.
-    Sugar(Sugar),
-}
-
-#[derive(Clone, Copy, Debug, PartialEq, Eq)]
-pub enum Sugar {
+    /// This call is the result of desugaring string interpolation,
+    /// e.g. "\(first) \(last)" is transformed into Str.concat (Str.concat first " ") last.
     StringInterpolation,
 }