Revert "Add CastContentWindow::SetCanGoBackQuery"

This reverts commit 8985ccdc.

Reason for revert: not needed, already plumbed through different path

Original change's description:
> Add CastContentWindow::SetCanGoBackQuery
> 
> This allows querying the CanGoBack status of the underlying app
> 
> Bug: b/145762033
> Test: None
> Change-Id: I330d7124dd7817db69f5ff41bfa58f6059971113
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008066
> Reviewed-by: Luke Halliwell (slow) <halliwell@chromium.org>
> Commit-Queue: Albert Chaulk <achaulk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#733446}

TBR=achaulk@chromium.org,dnicoara@chromium.org,halliwell@chromium.org,seantopping@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: b/145762033
Change-Id: I668bc87b91d7e70d70c04b995a98d6d756ad5808
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2013464Reviewed-by: Albert Chaulk <achaulk@chromium.org>
Commit-Queue: Albert Chaulk <achaulk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733739}

chromecast/browser/cast_content_window.cc

@@ -24,9 +24,6 @@ void CastContentWindow::RemoveObserver(Observer* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
-void CastContentWindow::SetCanGoBackQuery(
-    base::RepeatingCallback<bool()> can_go_back) {}
-
 mojom::MediaControlUi* CastContentWindow::media_controls() {
   return nullptr;
 }

chromecast/browser/cast_content_window.h

@@ -8,7 +8,6 @@
 #include <memory>
 #include <string>
 
-#include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
@@ -205,10 +204,6 @@ class CastContentWindow {
   // the window manager.
   virtual void SetHostContext(base::Value host_context) = 0;
 
-  // Set a callback that can be queried for if the owner can handle a "back"
-  // gesture. If not set the default is to assume that gestures are unhandled.
-  virtual void SetCanGoBackQuery(base::RepeatingCallback<bool()> can_go_back);
-
   // Notify the window that its visibility type has changed. This should only
   // ever be called by the window manager.
   // TODO(seantopping): Make this private to the window manager.