Avoid calling fail in tests

Summary:
Looks like we call fail() here which has special meaning in Jest tests but newer versions of Jest don't implement it, and our OSS test run in that newer version.
jestjs/jest#11698

Trying to see if it's possible to remove that call to fail() so that OSS and internal tests have consistent behavior.

Reviewed By: itamark

Differential Revision: D68867479

fbshipit-source-id: 896ffff042849dfff6fe7ff88d61084e20d369dd

packages/relay-runtime/network/RelayObservable.js

@@ -614,11 +614,7 @@ if (__DEV__) {
   // Default implementation of HostReportErrors() in development builds.
   // Can be replaced by the host application environment.
   RelayObservable.onUnhandledError((error, isUncaughtThrownError) => {
-    declare function fail(string): void;
-    if (typeof fail === 'function') {
-      // In test environments (Jest), fail() immediately fails the current test.
-      fail(String(error));
-    } else if (isUncaughtThrownError) {
+    if (isUncaughtThrownError) {
       // Rethrow uncaught thrown errors on the next frame to avoid breaking
       // current logic.
       setTimeout(() => {