[NTP] Fix dark mode not applying to custom link dialogs

Remove the now defunct configData.isDarkModeEnabled references.

Bug: 927955
Change-Id: Iba9c557eba265d1fa5f5eeaeeff5a2382bfbc26e
Reviewed-on: https://chromium-review.googlesource.com/c/1450756
Commit-Queue: Kristi Park <kristipark@chromium.org>
Reviewed-by: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#628531}

chrome/browser/resources/local_ntp/local_ntp.js

@@ -1168,7 +1168,7 @@ function createIframes() {
   args.push('removeTooltip=' +
       encodeURIComponent(configData.translatedStrings.removeThumbnailTooltip));
 
-  if (configData.isDarkModeEnabled) {
+  if (isDarkModeEnabled) {
     args.push('enableDarkMode=1');
   }
 
@@ -1206,7 +1206,7 @@ function createIframes() {
       clArgs.push('rtl=1');
     }
 
-    if (configData.isDarkModeEnabled) {
+    if (isDarkModeEnabled) {
       clArgs.push('enableDarkMode=1');
     }