Disable iframes filtering feature for supervised users

The feature has been disabled in Chrome OS < M87 with
Finch kill-switch and in this cl we apply the same change
in Chromium repo.

Bug: 1132862
Change-Id: I7c3446b6a6d7e4d06cdf2df5f12d6cf9eec4dc24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2435721Reviewed-by: Aga Wronska <agawronska@chromium.org>
Reviewed-by: Yilkal Abe <yilkal@chromium.org>
Auto-Submit: Aga Wronska <agawronska@chromium.org>
Commit-Queue: Yilkal Abe <yilkal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811255}

chrome/browser/supervised_user/supervised_user_features.cc

@@ -7,7 +7,7 @@
 namespace supervised_users {
 
 const base::Feature kSupervisedUserIframeFilter{
-    "SupervisedUserIframeFilter", base::FEATURE_ENABLED_BY_DEFAULT};
+    "SupervisedUserIframeFilter", base::FEATURE_DISABLED_BY_DEFAULT};
 
 const base::Feature kSupervisedUserInitiatedExtensionInstall{
     "SupervisedUserInitiatedExtensionInstall",