Remove unnecessary generic type arguments

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=175155365

java/google/registry/model/billing/RegistrarCreditBalance.java

@@ -211,7 +211,7 @@ public final class RegistrarCreditBalance extends ImmutableObject implements Bui
     private Optional<Money> getMostRecentlyWrittenBalance(
         Map.Entry<DateTime, ImmutableSortedMap<DateTime, Money>> balancesAtEffectiveTime) {
       return balancesAtEffectiveTime == null
-          ? Optional.<Money>empty()
+          ? Optional.empty()
           // Don't use Optional.ofNullable() here since it's an error if there's a empty submap.
           : Optional.of(balancesAtEffectiveTime.getValue().lastEntry().getValue());
     }