viz: Remove unused code in GLRenderer

Didn't find any implementation or caller, so remove one function.

Change-Id: Id8ffc1544dc7670622c68684405d681e04f518c8
Reviewed-on: https://chromium-review.googlesource.com/1118570Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: weiliangc <weiliangc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571362}

components/viz/service/display/gl_renderer.h

@@ -241,7 +241,6 @@ class VIZ_SERVICE_EXPORT GLRenderer : public DirectRenderer {
                            const gfx::QuadF* clip_region);
   void DrawYUVVideoQuad(const YUVVideoDrawQuad* quad,
                         const gfx::QuadF* clip_region);
-  void DrawOverlayCandidateQuadBorder(float* gl_matrix);
 
   void SetShaderOpacity(float opacity);
   void SetShaderQuadF(const gfx::QuadF& quad);