viewer: removed framebuffer that never got used

This framebuffer was an early approach to the pixel sampler that never got
used, but was still getting created/destroyed unnecessarily. This has now
been removed.

app/widget/viewer/viewerglwidget.cpp

@@ -142,17 +142,6 @@ void ViewerGLWidget::SetSignalCursorColorEnabled(bool e)
 {
   signal_cursor_color_ = e;
   setMouseTracking(e);
-
-  // Create frame buffer for reading from texture
-  if (e != frame_buffer_.IsCreated()) {
-    makeCurrent();
-    if (e) {
-      frame_buffer_.Create(context());
-    } else {
-      frame_buffer_.Destroy();
-    }
-    doneCurrent();
-  }
 }
 
 void ViewerGLWidget::SetImageFromLoadBuffer(Frame *in_buffer)

app/widget/viewer/viewerglwidget.h

@@ -224,11 +224,6 @@ private:
    */
   OpenGLColorProcessorPtr color_service_;
 
-  /**
-   * @brief Framebuffer used for reading reference space pixels from the texture
-   */
-  OpenGLFramebuffer frame_buffer_;
-
   /**
    * @brief Drawing matrix (defaults to identity)
    */