Remove local version from `@font-face`

It's unlikely that the bundled version wouldn't load, and it's
especially unlikely that the page would load but the bundled version
would not.

Also, if it doesn't load, it should fall back to another monospace font,
which is fine.

src/theme/fonts/fonts.css

@@ -96,6 +96,5 @@
   font-family: 'Source Code Pro';
   font-style: normal;
   font-weight: 500;
-  src: url('source-code-pro-v11-all-charsets-500.woff2') format('woff2'),
-       local('Source Code Pro Medium'), local('SourceCodePro-Medium');
+  src: url('source-code-pro-v11-all-charsets-500.woff2') format('woff2');
 }