Remove shared_ptr<GpuBuffer> member from GlTextureView

This only exists to support GlTexture's GetFrame API. It can be moved into GlTexture.

PiperOrigin-RevId: 488812896

mediapipe/gpu/gl_texture_view.cc

@@ -7,7 +7,6 @@ void GlTextureView::Release() {
   if (detach_) detach_(*this);
   detach_ = nullptr;
   gl_context_ = nullptr;
-  gpu_buffer_ = nullptr;
   plane_ = 0;
   name_ = 0;
   width_ = 0;