minor #27156 [FrameworkBundle] Remove dead code (chalasr)

This PR was merged into the 4.0 branch.

Discussion
----------

[FrameworkBundle] Remove dead code

| Q             | A
| ------------- | ---
| Branch?       | 4.0
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Commits
-------

29b3e31382 [FrameworkBundle] Remove dead code

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php

@@ -97,11 +97,6 @@ class FrameworkExtension extends Extension
     private $annotationsConfigEnabled = false;
     private $validatorConfigEnabled = false;
 
-    /**
-     * @var string|null
-     */
-    private $kernelRootHash;
-
     /**
      * Responds to the app.config configuration parameter.
      *
@@ -1391,20 +1386,6 @@ class FrameworkExtension extends Extension
         }
     }
 
-    /**
-     * Gets a hash of the kernel root directory.
-     *
-     * @return string
-     */
-    private function getKernelRootHash(ContainerBuilder $container)
-    {
-        if (!$this->kernelRootHash) {
-            $this->kernelRootHash = hash('sha256', $container->getParameter('kernel.root_dir'));
-        }
-
-        return $this->kernelRootHash;
-    }
-
     /**
      * Returns the base path for the XSD files.
      *