Remove deprecated fields from CustomerUsage type

The onDemandMaxSpend and onDemandEventsAllowed fields on the customer
usage endpoint response have been deprecated since 2022 and are not
read by any frontend consumer.

Author: noahsmartin

static/gsApp/types/index.tsx

@@ -571,8 +571,6 @@ export type BillingStatTotal = {
 };
 
 export type CustomerUsage = {
-  onDemandEventsAllowed: number;
-  onDemandMaxSpend: number;
   periodEnd: string;
   periodStart: string;
   stats: Record<string, BillingStats>;

tests/js/getsentry-test/fixtures/customerUsage.ts

@@ -8,8 +8,6 @@ export function CustomerUsageFixture(
   return {
     periodStart: '2022-06-01',
     periodEnd: '2022-06-30',
-    onDemandMaxSpend: 0,
-    onDemandEventsAllowed: 0,
     totals: {
       errors: UsageTotalFixture(),
       transactions: UsageTotalFixture(),