Remove leftover checking of a removed flag in editing/spelling/spellcheck-queue.html

The web tests checks runtime flag idleSpellCheckingCallbackEnabled, which
is a removed flag after shipping of idle time spellchecker.

Hence, this patch removes the checking of the flag.

Change-Id: Ie8f279854a2b7625d7b526bfe0e50534cf9f8891
Reviewed-on: https://chromium-review.googlesource.com/c/1351872Reviewed-by: Kent Tamura <tkent@chromium.org>
Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Xiaocheng Hu <xiaochengh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611302}

third_party/blink/web_tests/editing/spelling/spellcheck-queue.html

@@ -6,7 +6,7 @@
 
 <script>
 function runIdleTimeSpellCheckerIfNeeded(document) {
-  if (!window.internals || !internals.runtimeFlags.idleSpellCheckCallbackEnabled)
+  if (!window.internals)
     return;
   internals.runIdleTimeSpellChecker(document);
 }