fix(stream-presenter-effect): Prevent memory leak.

On electron 7 drawing on hidden canvas will trigger a memory leak.
Not appending the canvas for the DOM seems to solve the problem.

react/features/stream-effects/presenter/JitsiStreamPresenterEffect.js

         this._canvas = document.createElement('canvas');
         this._ctx = this._canvas.getContext('2d');
 
-        if (document.body !== null) {
-            document.body.appendChild(this._canvas);
-        }
         this._desktopElement = document.createElement('video');
         this._videoElement = document.createElement('video');
         videoDiv.appendChild(this._videoElement);