[ios] Show error page over content filter webkit errors.

iOS 12.2 has a bug where the WKWebView internal page doesn't display.

Bug: 950488, 793317
Change-Id: Idf3e26125b121a7b753f65e176337f5fc67ce2ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1562218
Reviewed-by: Eugene But <eugenebut@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Auto-Submit: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649632}

ios/web/web_state/ui/crw_web_controller.mm

@@ -5235,13 +5235,6 @@ - (void)handleLoadError:(NSError*)error
       return;
     }
 
-    if (error.code == web::kWebKitErrorUrlBlockedByContentFilter &&
-        web::GetWebClient()->IsSlimNavigationManagerEnabled()) {
-      // If URL is blocked due to Restriction, do not take any further action as
-      // WKWebView will show a built-in error.
-      return;
-    }
-
     if (error.code == web::kWebKitErrorFrameLoadInterruptedByPolicyChange) {
       // This method should not be called if the navigation was cancelled by
       // embedder.