Remove constructor and clear method call from TreeMapDB class

on-behalf-of: @Mermaid-Chart <hello@mermaidchart.com>

packages/mermaid/src/diagrams/treemap/db.ts

@@ -21,10 +21,6 @@ export class TreeMapDB implements DiagramDB {
   private classes: Map<string, DiagramStyleClassDef> = new Map<string, DiagramStyleClassDef>();
   private root?: TreemapNode;
 
-  constructor() {
-    this.clear();
-  }
-
   public getNodes() {
     return this.nodes;
   }