chore: subgraph refactor

Author: shotaronowhere

subgraph/schema.graphql

@@ -154,10 +154,9 @@ type Dispute @entity {
   currentRuling: BigInt!
   tied: Boolean!
   overridden: Boolean!
-  periodDeadline: BigInt! # uint256j
+  periodDeadline: BigInt!
   periodNotificationIndex: BigInt!
   lastPeriodChangeTs: BigInt!
-  lastPeriodChangeBlock: BigInt!
   lastPeriodChangeBlockNumber: BigInt!
   rounds: [Round!]! @derivedFrom(field: "dispute")
   currentRound: Round!

subgraph/src/entities/Dispute.ts

@@ -18,7 +18,6 @@ export function createDisputeFromEvent(event: DisputeCreation): void {
   dispute.tied = true;
   dispute.overridden = false;
   dispute.lastPeriodChangeTs = event.block.timestamp;
-  dispute.lastPeriodChangeBlock = event.block.timestamp;
   dispute.lastPeriodChangeBlockNumber = event.block.number;
   let counter = PeriodIndexCounter.load("evidence");
   if (!counter) {