[Code health] Remove a dead function declaration

There is no definition of this function.

Bug: None
Change-Id: I51f25306a794bfe55612ad90500f9538643a85c4
Reviewed-on: https://chromium-review.googlesource.com/c/1335829Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607997}

content/renderer/render_widget.h

@@ -725,13 +725,6 @@ class CONTENT_EXPORT RenderWidget
 
   gfx::ColorSpace GetRasterColorSpace() const;
 
-  void SendInputEventAck(blink::WebInputEvent::Type type,
-                         uint32_t touch_event_id,
-                         InputEventAckState ack_state,
-                         const ui::LatencyInfo& latency_info,
-                         std::unique_ptr<ui::DidOverscrollParams>,
-                         base::Optional<cc::TouchAction>);
-
   void UpdateZoom(double zoom_level);
 
 #if BUILDFLAG(ENABLE_PLUGINS)