Don't load `compatibility.js` in the viewer while in non-`PRODUCTION` mode

At this point, the default viewer is already not usable in older browsers in `gulp server` mode, since we only run the code through Babel as part of the build step.
Hence there shouldn't be much point in manually loading `compatibility.js` in `viewer.html` the way that we've been doing, especially considering that it's already being loaded by `src/shared/util.js`.

web/viewer.html

@@ -44,10 +44,6 @@ See https://github.com/adobe-type-tools/cmap-resources
     <link rel="resource" type="application/l10n" href="locale/locale.properties">
 <!--#endif-->
 
-<!--#if !PRODUCTION-->
-    <script src="../src/shared/compatibility.js"></script>
-<!--#endif-->
-
 <!--#if !PRODUCTION-->
     <script src="../node_modules/systemjs/dist/system.js"></script>
     <script src="../systemjs.config.js"></script>