Remove spurious @Nullable

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=136160050

java/google/registry/model/registry/Registry.java

@@ -571,7 +571,6 @@ public class Registry extends ImmutableObject implements Buildable {
     return nullToEmptyImmutableCopy(allowedFullyQualifiedHostNames);
   }
 
-  @Nullable
   public Interval getLrpPeriod() {
     return (lrpPeriodStart == null && lrpPeriodEnd == null)
         ? new Interval(START_OF_TIME, Duration.ZERO)