Fix footer background issues in the blog index.

Summary:
Fixes #10091.

Some now unused CSS is removed here as well.
Closes https://github.com/facebook/react-native/pull/10092

Differential Revision: D3919399

Pulled By: hramos

fbshipit-source-id: ed29c4a3e1ba01d930013db04862bce3fa4c5cbb

website/core/Site.js

@@ -128,7 +128,7 @@ var Site = React.createClass({
 
             {this.props.children}
 
-            <footer>
+            <footer className="nav-footer">
               <section className="sitemap">
                 <a href="/react-native" className="nav-home">
                   <img src="img/header_logo.png" alt="React Native" width="66" height="58" />

website/src/react-native/css/react-native.css

@@ -756,14 +756,6 @@ h1:hover .hash-link, h2:hover .hash-link, h3:hover .hash-link, h4:hover .hash-li
   float: right;
 }
 
-footer.wrap {
-  font-size: 13px;
-  font-weight: 600;
-  padding-top: 36px;
-  padding-bottom: 18px;
-  overflow: auto;
-}
-
 section.black content {
   padding-bottom: 18px;
 }
@@ -1852,7 +1844,7 @@ article li {
 
 /** Footer **/
 
-footer {
+footer.nav-footer {
   box-sizing: border-box;
   border: none;
   font-weight: 300;