Event: shouldn't use Sizzle on non-element nodes. Fixes #14986.

I described the bug here: http://bugs.jquery.com/ticket/14986

There's also a corresponding Sizzle PR https://github.com/jquery/sizzle/pull/256, but I think the consensus there is that it could be a jQuery core bug. The minimal test case relies on DOMNodeRemoved, which is deprecated in a lot of browsers, but a lot of it is still living in the wild wild web, so perhaps it makes sense to fix this.

Happy to work on it a bit more!