Re-enable testBundleURL test in open source

Summary:
The `testBundleURL` test was disabled in open source recently due to issues running it successfully in Facebook's internal CI. We're now skipping `RCTBundleURLProviderTests` tests internally, so it's safe to re-enable now and ensure it runs in Circle CI.

Changelog:

[iOS] [Changed] - Re-enable testBundleURL unit test.

Reviewed By: cpojer

Differential Revision: D15140192

fbshipit-source-id: 5f6a91f3ce8cea245be31dff3ffb86768deab0be

RNTester/RNTesterUnitTests/RCTBundleURLProviderTests.m

@@ -71,10 +71,8 @@ - (void)testBundleURL
   NSURL *URL = [settings jsBundleURLForBundleRoot:testFile fallbackResource:nil];
   if (!getenv("CI_USE_PACKAGER")) {
     XCTAssertEqualObjects(URL, mainBundleURL());
-    // TODO: t43430850: Temporarily disable testBundleURL test.
-    // To be re-enabled when the packager can be reliably used on Sandcastle.
-    // } else {
-    //   XCTAssertEqualObjects(URL, localhostBundleURL());
+  } else {
+    XCTAssertEqualObjects(URL, localhostBundleURL());
   }
 }