remove check for invalid rates, as it isn't valid for L2

This check calls Issuer.availableCurrencyKeys, which will miss some assets that
are required to have exchange rates but aren't technically enabled for issuing yet
on L2.

test/integration/utils/rates.js

@@ -4,9 +4,7 @@ const { toBytes32 } = require('../../..');
 async function updateExchangeRatesIfNeeded({ ctx }) {
 	const { Synthetix, DebtCache } = ctx.contracts;
 
-	if (await Synthetix.anySynthOrSNXRateIsInvalid()) {
 	await _simulateExchangeRates({ ctx });
-	}
 
 	const { isInvalid, isStale } = await DebtCache.cacheInfo();
 	if (isInvalid || isStale) {