title: Remove 'a' from legend when using aesthetics and geom_text
body: <p>How can I can remove the letter 'a' from the legend generated by this code? If I remove the <code>geom_text</code>, then the 'a' letter will not show in the legend. I want to keep <code>geom_text</code>, though.</p>
  <pre><code>ggplot(data = iris, aes(x = Sepal.Length, y=Sepal.Width, 
                          shape = Species, colour = Species)) + 
     geom_point() + 
     geom_text(aes(label = Species))
  </code></pre>