NFC: Address Clippy `clone_on_copy`.

mk/clippy.sh

@@ -26,7 +26,6 @@ cargo clippy \
   \
   --deny clippy::as_conversions \
   \
-  --allow clippy::clone_on_copy \
   --allow clippy::explicit_auto_deref \
   --allow clippy::too_many_arguments \
   $NULL

src/name/dns_name.rs

@@ -125,7 +125,7 @@ impl<'a> DnsNameRef<'a> {
     pub fn to_owned(&self) -> DnsName {
         // DnsNameRef is already guaranteed to be valid ASCII, which is a
         // subset of UTF-8.
-        let s: &str = self.clone().into();
+        let s: &str = (*self).into();
         DnsName(s.to_ascii_lowercase())
     }
 }