Bug 1458567 part 2 - Remove now unnecessary dom.max_chrome_script_run_time entry from browser_preferences_usage.js test. r=johannh

browser/base/content/test/performance/browser_preferences_usage.js

@@ -93,10 +93,6 @@ add_task(async function startup() {
       min: 10,
       max: 55,
     },
-    "dom.max_chrome_script_run_time": {
-      min: 20,
-      max: 55,
-    },
   };
 
   let startupRecorder = Cc["@mozilla.org/test/startuprecorder;1"].getService().wrappedJSObject;