Remove the bulk of the WebGL legacy code.

Things left to do:
* redo an icon layer example
* redo a clipping layer example
* update docs where WebGL renderers are mentioned

examples/side-by-side.css

@@ -1,7 +0,0 @@
-@media (min-width: 800px) {
-  .half {
-    padding: 0 10px;
-    width: 50%;
-    float: left;
-  }
-}