title: Delete annotation from figure
body: <p>I have a gui that includes a plot. In this plot I add an annotation. When the plot data is changed using the gui, he old annotation remains and the new one is plotted over the old on.</p>
  
  <p>So I need to remove he old annotation.
  I tried the following code, but that has no effect:</p>
  
  <pre><code>set(0,'showhiddenhandles','on')
  % look for all axes in the figure of choice:
  h_all_axes = findall(gcf,'type','axes');
  % get the 'annotation layer' axes handle:
  h_anno_axes = double(find(handle(h_all_axes),'-class','graph2d.annotationlayer'));
  delete(h_anno_axes);
  set(0,'showhiddenhandles','off');
  
  annotationPos = [0.55 0.58 0.6 0.3];
  htxtbox = annotation('textbox',annotationPos, ...
      'String'     ,strtextbox, ...
      'FontSize'   ,FontSize+1, ...
      'FitBoxToText', 'on', ...
      'EdgeColor', 'none', ...
      'FontName'   , 'Courier New');
  </code></pre>