Bug 1750915 - [devtools] Remove backward compatible code for frame.isTopLevel. r=jdescottes

Differential Revision: https://phabricator.services.mozilla.com/D136345

devtools/client/framework/toolbox.js

@@ -3355,11 +3355,6 @@ Toolbox.prototype = {
 
     try {
       const { frames } = await this.target.listFrames();
-
-      // @backward-compat { version 96 } frame.isTopLevel was added in 96.
-      for (const frame of frames) {
-        frame.isTopLevel = !frame.parentID;
-      }
       this._updateFrames({ frames });
     } catch (e) {
       console.error("Error while listing frames", e);

devtools/client/fronts/targets/window-global.js

@@ -61,9 +61,7 @@ class WindowGlobalTargetFront extends TargetMixin(
    * Event listener for `frameUpdate` event.
    */
   _onFrameUpdate(packet) {
-    // @backward-compat { version 96 } isTopLevel was added on the server in 96, so we
-    // can simply send `packet` when 96 hits release.
-    this.emit("frame-update", { ...packet, isTopLevel: !packet.parentID });
+    this.emit("frame-update", packet);
   }
 
   /**