Remove ReactBrowserComponent dependency from ReactTextComponent

It's no longer used as of #1598, which just missed the require.

Test Plan: build, jest

src/browser/ReactTextComponent.js

@@ -20,7 +20,6 @@
 "use strict";
 
 var DOMPropertyOperations = require('DOMPropertyOperations');
-var ReactBrowserComponentMixin = require('ReactBrowserComponentMixin');
 var ReactComponent = require('ReactComponent');
 var ReactElement = require('ReactElement');