Revert "[Fuchsia] Implement extra headers support in NavigationController."

This reverts commit c6df4d27.

Reason for revert: Broke Fuchsia browsertests.
Bug: 925574

Original change's description:
> [Fuchsia] Implement extra headers support in NavigationController.
> 
> This implements setting and using the |headers| data in
> LoadUrlParams. A new test fixture is added to ensure the extra headers
> are properly received by the test server.
> 
> Bug: 923598
> Change-Id: I59a44c886f1853bbc631ae016b0655dd1d4d539b
> Reviewed-on: https://chromium-review.googlesource.com/c/1427565
> Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
> Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#625912}

TBR=wez@chromium.org,kmarshall@chromium.org,fdegans@chromium.org

Change-Id: I82c9a5dead06edd58553a0999b708c6cc8b8dfd7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 923598
Reviewed-on: https://chromium-review.googlesource.com/c/1437914Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626277}

fuchsia/browser/frame_impl.cc

@@ -295,16 +295,6 @@ void FrameImpl::LoadUrl(std::string url,
 
   content::NavigationController::LoadURLParams params_converted(validated_url);
 
-  if (!params->headers.empty()) {
-    std::vector<base::StringPiece> extra_headers;
-    extra_headers.reserve(params->headers.size());
-    for (const auto& header : params->headers) {
-      extra_headers.push_back(base::StringPiece(
-          reinterpret_cast<const char*>(header.data()), header.size()));
-    }
-    params_converted.extra_headers = base::JoinString(extra_headers, "\n");
-  }
-
   if (validated_url.scheme() == url::kDataScheme)
     params_converted.load_type = content::NavigationController::LOAD_TYPE_DATA;