Bug 1603176: Remove unused variable. r=jdescottes

Differential Revision: https://phabricator.services.mozilla.com/D61346

--HG--
extra : moz-landing-system : lando

devtools/client/memory/panel.js

@@ -31,7 +31,6 @@ MemoryPanel.prototype = {
     }
 
     this.panelWin.gToolbox = this._toolbox;
-    this.panelWin.gTarget = this.target;
     this.panelWin.gFront = await this.target.getFront("memory");
     this.panelWin.gHeapAnalysesClient = new HeapAnalysesClient();