refactor: Remove TogglesHeadlessMode redundant methods

laravel/dusk#1098

Laravel Dusk 8.x now defines these methods in class
Laravel\Dusk\TestCase so the stub classes that extend
TestCase don't need to redefine hasHeadlessDisabled()
and shouldStartMaximized().

src/Concerns/TogglesHeadlessMode.php

@@ -19,26 +19,4 @@ protected function filterHeadlessArguments(array $args = [])
             ]);
         })->values()->all();
     }
-
-    /**
-     * Determine whether the Dusk command has disabled headless mode.
-     *
-     * @return bool
-     */
-    protected function hasHeadlessDisabled()
-    {
-        return isset($_SERVER['DUSK_HEADLESS_DISABLED']) ||
-               isset($_ENV['DUSK_HEADLESS_DISABLED']);
-    }
-
-    /**
-     * Determine if the browser window should start maximized.
-     *
-     * @return bool
-     */
-    protected function shouldStartMaximized()
-    {
-        return isset($_SERVER['DUSK_START_MAXIMIZED']) ||
-               isset($_ENV['DUSK_START_MAXIMIZED']);
-    }
 }