[ChromeDriver] Remove checking Page.interstitialShown from navigation_tracker

Bug: chromedriver:3155
Change-Id: I545ab145a03eef9e79b38560767bda05608f12f1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1872626Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Tatiana Buldina <buldina@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707965}

chrome/test/chromedriver/chrome/navigation_tracker.cc

@@ -198,9 +198,6 @@ Status NavigationTracker::OnEvent(DevToolsClient* client,
     }
   } else if (method == "Inspector.targetCrashed") {
     loading_state_ = kNotLoading;
-  } else if (method == "Page.interstitialShown") {
-    client_->SendCommandAndIgnoreResponse("Page.stopLoading", {});
-    return Status(kUnexpectedAlertOpen, "Interstitial popups not supported");
   }
   if (timed_out_)
     loading_state_ = kNotLoading;