Allow unmounting title tag

cf. facebook#1376.

This is useful for SVG. Dynamically adding and removing `<title>` elements in SVG still won't work properly because of getMarkupWrap but this at least lets you include it in initial render and then unmount the entire `<svg>` without problems.

src/browser/ui/ReactDefaultInjection.js

@@ -87,7 +87,6 @@ function inject() {
 
     html: createFullPageComponent(ReactDOM.html),
     head: createFullPageComponent(ReactDOM.head),
-    title: createFullPageComponent(ReactDOM.title),
     body: createFullPageComponent(ReactDOM.body)
   });