feat!(derive): no push for repeated enum fields

With OpenEnum wrapping the scalar values, the push method
no longer provides enough utility.

prost-derive/src/field/scalar.rs

@@ -290,8 +290,6 @@ impl Field {
                         "Returns an iterator which yields the valid enum values contained in `{}`.",
                         ident_str,
                     );
-                    let push = Ident::new(&format!("push_{}", ident_str), Span::call_site());
-                    let push_doc = format!("Appends the provided enum value to `{}`.", ident_str);
                     let wrapped_ty = quote!(::prost::OpenEnum<#ty>);
                     Some(quote! {
                         #[doc=#iter_doc]
@@ -301,10 +299,6 @@ impl Field {
                         > {
                             self.#ident.iter().cloned().filter_map(|x| { x.known() })
                         }
-                        #[doc=#push_doc]
-                        pub fn #push(&mut self, value: #ty) {
-                            self.#ident.push(value.into());
-                        }
                     })
                 }
                 _ => None,