Remove empty TextNode left behind by IE8 setInnerHTML workaround

What the title says, if it appends the `\uFEFF` to fix whitespace it can end up leaving an empty TextNode behind. This is very bad because it offsets the index of children. Also, `renderComponent` still uses `firstChild` which causes it to see the TextNode and replace the content rather than update it as it should.

@zpao We definitely want to merge this sooner rather than later.
@zpao My intention here was that this only targets IE8, which does support it. As I mentioned somewhere else, we could change the feature test to just `document.documentMode === 8`, if some other old browser flunks the test, I *really* doubt that this trickery would fix it.