Change RESTORE BillingEvents to have 1-year periods

This simplifies calculating the overall invoice by giving RESTORE fees a
period equal to the period of the associated RENEW (1 year). Older
BillingEvents will not be backfilled, and will have periodYears = null.

Invoicing and business both agree this is a valid representation, since RESTORE fees are intrinsically tied to the 1-year RENEW it's associated with.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=188041777

java/google/registry/flows/domain/DomainRestoreRequestFlow.java

@@ -239,7 +239,6 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
   private OneTime createRenewBillingEvent(
       HistoryEntry historyEntry, Money renewCost, DateTime now) {
     return prepareBillingEvent(historyEntry, renewCost, now)
-        .setPeriodYears(1)
         .setReason(Reason.RENEW)
         .build();
   }
@@ -257,6 +256,7 @@ public final class DomainRestoreRequestFlow implements TransactionalFlow  {
         .setClientId(clientId)
         .setEventTime(now)
         .setBillingTime(now)
+        .setPeriodYears(1)
         .setCost(cost)
         .setParent(historyEntry);
   }