dbusServices/screencast: Removed unused properties

Those have been superseded by corresponding state enums.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2165>

js/dbusServices/screencast/screencastService.js

@@ -49,9 +49,6 @@ var Recorder = class {
         this._onErrorCallback = onErrorCallback;
         this._stopInvocation = null;
 
-        this._pipelineIsPlaying = false;
-        this._sessionIsActive = false;
-
         this._x = x;
         this._y = y;
         this._width = width;