Fix mindmap demo

demos/mindmap.html

@@ -40,7 +40,6 @@
 
     <script type="module">
       import mermaid from './mermaid.esm.mjs';
-      import mermaidMindmap from './mermaid-mindmap.esm.mjs';
 
       const ALLOWED_TAGS = [
         'a',
@@ -82,7 +81,6 @@
       mermaid.parseError = function (err, hash) {
         // console.error('Mermaid error: ', err);
       };
-      await mermaid.registerExternalDiagrams([mermaidMindmap]);
       mermaid.initialize({
         theme: 'base',
         startOnLoad: true,