Serve favicons along with our Gatsby static assets

There's no good reason to call these files out specifically in app.js or
handle them with special packages like serve-favicon.

package.json

@@ -54,7 +54,6 @@
     "query-string": "^4.2.3",
     "react-icons": "^3.11.0",
     "request": "^2.88.0",
-    "serve-favicon": "^2.5.0",
     "session-file-store": "^1.3.1",
     "yaml-front-matter": "^4.0.0"
   },

src/app.js

@@ -2,7 +2,6 @@
 const sslRedirect = require('heroku-ssl-redirect');
 const nakedRedirect = require('express-naked-redirect');
 const express = require("express");
-const favicon = require('serve-favicon');
 const compression = require('compression');
 const utils = require("./utils");
 const cors = require('cors');
@@ -13,7 +12,7 @@ const production = process.env.NODE_ENV === "production";
 
 const charon = require("./endpoints/charon");
 const users = require("./endpoints/users");
-const {assetPath, auspiceAssets, gatsbyAssets, sendAuspiceEntrypoint, sendGatsbyEntrypoint, sendGatsbyPage, sendGatsby404} = require("./endpoints/static");
+const {auspiceAssets, gatsbyAssets, sendAuspiceEntrypoint, sendGatsbyEntrypoint, sendGatsbyPage, sendGatsby404} = require("./endpoints/static");
 const {setSource, setGroupSource, setDataset, setNarrative, canonicalizeDataset, ifDatasetExists, ifNarrativeExists} = require("./endpoints/sources");
 const authn = require("./authn");
 const redirects = require("./redirects");
@@ -35,8 +34,6 @@ if (production) app.enable("trust proxy");
 app.use(sslRedirect()); // redirect HTTP to HTTPS
 app.use(compression()); // send files (e.g. res.json()) using compression (if possible)
 app.use(nakedRedirect({reverse: true})); // redirect www.nextstrain.org to nextstrain.org
-app.use(favicon(assetPath("favicon.ico")));
-app.use('/favicon.png', express.static(assetPath("favicon.png")));
 
 
 /* Setup a request-scoped context object for passing arbitrary request-local

src/endpoints/static.js

@@ -6,7 +6,7 @@ const path = require("path");
 const utils = require("../utils");
 
 
-/* Path helpers for static assets, to make routes more readable.
+/* Path helpers for our handlers below.
  */
 const assetPath = (...subpath) =>
   path.join(__dirname, "..", "..", ...subpath);
@@ -157,7 +157,6 @@ const sendGatsby404 = async (req, res) => {
 
 
 module.exports = {
-  assetPath,
   auspiceAssets,
   gatsbyAssets,
 

static-site/src/html.jsx

@@ -2,7 +2,7 @@
 /* eslint import/extensions:"off" */
 /* eslint global-require:"off" */
 import React from "react";
-import favicon from "../../favicon.png";
+import favicon from "../static/favicon.png";
 
 // eslint-disable-next-line react/prefer-stateless-function
 export default class HTML extends React.Component {