Fix output handling logic in graph.rs

Removed unnecessary conditional check for multiple outputs, streamlining the code. This change ensures consistent handling of output types and reduces complexity in the logic.

crates/burn-import/src/burn/graph.rs

@@ -472,15 +472,7 @@ impl<PS: PrecisionSettings> BurnGraph<PS> {
         self.graph_output_types.iter().for_each(|output| {
             let name = output.name();
             let ty = output.ty();
-
-            if multiple_output {
-                output_type_def.extend(quote! {
-                    #ty,
-                });
-                output_return_def.extend(quote! {
-                    #name,
-                });
-            } else {
+            {
                 output_type_def.extend(quote! {
                     #ty
                 });