feature #24239 [HttpFoundation] Deprecate compatibility with PHP <5.4 sessions (afurculita)

This PR was squashed before being merged into the 3.4 branch (closes #24239).

Discussion
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[HttpFoundation] Deprecate compatibility with PHP <5.4 sessions

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

This PR removes functionality added in Symfony 2.1 as a compatibility layer with sessions from PHP <5.4.

- [x] Fix tests

Commits
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3deb3940ab [HttpFoundation] Deprecate compatibility with PHP <5.4 sessions

Author: Tobion

Tests/Controller/ControllerTraitTest.php

@@ -376,7 +376,7 @@ public function testRedirectToRoute()
     public function testAddFlash()
     {
         $flashBag = new FlashBag();
-        $session = $this->getMockBuilder('Symfony\Component\HttpFoundation\Session\Session')->getMock();
+        $session = $this->getMockBuilder('Symfony\Component\HttpFoundation\Session\Session')->disableOriginalConstructor()->getMock();
         $session->expects($this->once())->method('getFlashBag')->willReturn($flashBag);
 
         $container = new Container();