rust(lint): remove useless format calls

In these simple cases to_string() is recommended and likely
performs better as the formatter is not called.

rust/src/ike/logger.rs

@@ -29,7 +29,7 @@ fn add_attributes(transform: &Vec<SaAttribute>, js: &mut JsonBuilder) -> Result<
     for attribute in transform {
         js.set_string(
             attribute.attribute_type.to_string().as_str(),
-            format!("{}", attribute.attribute_value.to_string()).as_str(),
+            attribute.attribute_value.to_string().as_str(),
         )?;
 
         if let Some(numeric_value) = attribute.numeric_value {

rust/src/krb/log.rs

@@ -35,7 +35,7 @@ fn krb5_log_response(jsb: &mut JsonBuilder, tx: &mut KRB5Transaction) -> Result<
         None        => "<empty>".to_owned(),
     };
     let realm = match tx.realm {
-        Some(ref x) => format!("{}", x.0),
+        Some(ref x) => x.0.to_string(),
         None        => "<empty>".to_owned(),
     };
     let sname = match tx.sname {