Remove useless nav bar, always load cred explorer (#503)

There's no sense having a landing page with no content and
a nav bar with only one meaningful options. We can re-add
them later if we actually need navigation

Test plan: Local testing

src/app/App.js

@@ -1,38 +1,11 @@
 // @flow
 
 import React from "react";
-import {BrowserRouter as Router, Route, NavLink} from "react-router-dom";
 
 import CredExplorer from "./credExplorer/App";
 
 export default class App extends React.Component<{}> {
   render() {
-    const CRED_EXPLORER_ROUTE = "/explorer";
-    return (
-      <Router>
-        <React.Fragment>
-          <nav>
-            <ul>
-              <li>
-                <NavLink to="/">Home</NavLink>
-              </li>
-              <li>
-                <NavLink to={CRED_EXPLORER_ROUTE}>Cred Explorer</NavLink>
-              </li>
-            </ul>
-          </nav>
-
-          <hr />
-          <Route exact path="/" component={Home} />
-          <Route path={CRED_EXPLORER_ROUTE} component={CredExplorer} />
-        </React.Fragment>
-      </Router>
-    );
+    return <CredExplorer />;
   }
 }
-
-const Home = () => (
-  <div>
-    <h1>Welcome to SourceCred! Please make yourself at home.</h1>
-  </div>
-);