Remove reference to icons8 in about.html

We've stopped using icons8 as far as I can tell, instead using Google's material design icons.

Author: ethanmad

app/src/main/assets/about.html

@@ -32,6 +32,3 @@ <h4>Original Developer and 2013-14 Project Manager</h4>
 <h3>CREDITS</h3>
 iHW app icon made by <a href="https://plus.google.com/117749894688129225826/posts">REM Designs</a>.
 See more <a href=https://plus.google.com/communities/101391538081027754644>here.</a>
-
-<p>This application uses icons from <a href="http://www.icons8.com">icons8.com</a> (CC-BY-ND 3.0).
-</p>