Remove IE8-specific focus polyfill

[gaearon]

It looked like this:

function focusNode(node) {
  // IE8 can throw "Can't move focus to the control because it is invisible,
  // not enabled, or of a type that does not accept the focus." for all kinds of
  // reasons that are too expensive and fragile to test.
  try {
    node.focus();
  } catch (e) {}
}

We know it's definitely a node because we previously checked containsNode on document.documentElement with it.

So this should always be safe to call now.

[jquense]

does this get called with svg elements? We've had issues in the past with versions of IE not having focus methods

[jquense]

looks like its just inputs getting hit here :P so probably gtg