Don't generate obsolete charset attrs in <script>.

According to the HTML specification[1], the charset attribute is obsolete in
script elements.

[1]: https://html.spec.whatwg.org/multipage/obsolete.html#HTMLScriptElement-partial

Author: averms

src/theme/index.hbs

@@ -269,22 +269,22 @@
         {{/if}}
 
         {{#if playground_js}}
-        <script src="{{ path_to_root }}ace.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}editor.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}mode-rust.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}theme-dawn.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}theme-tomorrow_night.js" charset="utf-8"></script>
+        <script src="{{ path_to_root }}ace.js"></script>
+        <script src="{{ path_to_root }}editor.js"></script>
+        <script src="{{ path_to_root }}mode-rust.js"></script>
+        <script src="{{ path_to_root }}theme-dawn.js"></script>
+        <script src="{{ path_to_root }}theme-tomorrow_night.js"></script>
         {{/if}}
 
         {{#if search_js}}
-        <script src="{{ path_to_root }}elasticlunr.min.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}mark.min.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}searcher.js" charset="utf-8"></script>
+        <script src="{{ path_to_root }}elasticlunr.min.js"></script>
+        <script src="{{ path_to_root }}mark.min.js"></script>
+        <script src="{{ path_to_root }}searcher.js"></script>
         {{/if}}
 
-        <script src="{{ path_to_root }}clipboard.min.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}highlight.js" charset="utf-8"></script>
-        <script src="{{ path_to_root }}book.js" charset="utf-8"></script>
+        <script src="{{ path_to_root }}clipboard.min.js"></script>
+        <script src="{{ path_to_root }}highlight.js"></script>
+        <script src="{{ path_to_root }}book.js"></script>
 
         <!-- Custom JS scripts -->
         {{#each additional_js}}