Revert "Launch the `navigate-to` directive"

This reverts commit ceaafd48.

Reason for revert: likely cause of clusterfuzz crash

Original change's description:
> Launch the `navigate-to` directive
>
> The directive has been behind a flag for a year and we have received
> no [negative] feedback.
>
> Spec: https://w3c.github.io/webappsec-csp/#directive-navigate-to
>
> I2S: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/EJ4xF_DwZyk
>
> Bug: 805886
> Change-Id: I746aed4032149b86a5f9974246e2ec35bf8eb356
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1856100
> Reviewed-by: Andy Paicu <andypaicu@chromium.org>
> Reviewed-by: Mike West <mkwst@chromium.org>
> Commit-Queue: Andy Paicu <andypaicu@chromium.org>
> Auto-Submit: Andy Paicu <andypaicu@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#750183}

TBR=mkwst@chromium.org,andypaicu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.
TBR=mkwst@chromium.org

Bug: 805886
Change-Id: I03090af2eaee38c57084b4f0d8d0307e9d8e72aa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107486
Commit-Queue: Andy Paicu <andypaicu@chromium.org>
Reviewed-by: Andy Paicu <andypaicu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#751289}

third_party/blink/renderer/core/loader/frame_loader.cc

@@ -700,7 +700,8 @@ void FrameLoader::StartNavigation(FrameLoadRequest& request,
   mojo::PendingRemote<mojom::blink::NavigationInitiator> navigation_initiator;
   WTF::Vector<network::mojom::blink::ContentSecurityPolicyPtr> initiator_csp;
   network::mojom::blink::CSPSourcePtr initiator_self_source;
-  if (origin_document) {
+  if (origin_document && origin_document->GetContentSecurityPolicy()
+                             ->ExperimentalFeaturesEnabled()) {
     initiator_csp = origin_document->GetContentSecurityPolicy()
                         ->ExposeForNavigationalChecks();
     initiator_self_source = origin_document->GetContentSecurityPolicy()