Remove a:focus outline normalization

My hypothesis is that it's more important for a user to get the focus
style they expect *within* their browser than it is to have consistent focus
styles *between* browsers. In particular, replacing Chrome's default focus
style (esp. just for links) seems presumptuous.

Component designers/developers can make the decision on when to modify
these browser defaults.

Fix gh-216

normalize.css

@@ -90,14 +90,6 @@ a {
     background: transparent;
 }
 
-/**
- * Address `outline` inconsistency between Chrome and other browsers.
- */
-
-a:focus {
-    outline: thin dotted;
-}
-
 /**
  * Improve readability when focused and also mouse hovered in all browsers.
  */