Merge branch '2.7' into 2.8

* 2.7:
  Remove some unused variables, properties and methods
  [ExpressionLanguage] Fix parse error on 5.3
  [HttpKernel] remove noisy frame in controller stack traces
  [ExpressionLanguage] throw an SyntaxError instead of letting a undefined index notice
  Fix php doc in Table class
  bumped Symfony version to 2.7.40
  updated VERSION for 2.7.39
  update CONTRIBUTORS for 2.7.39
  updated CHANGELOG for 2.7.39

Author: nicolas-grekas

Extension/Core/Type/TimezoneType.php

@@ -23,13 +23,6 @@ class TimezoneType extends AbstractType
      */
     private static $timezones;
 
-    /**
-     * Stores the available timezone choices.
-     *
-     * @var array
-     */
-    private static $flippedTimezones;
-
     /**
      * {@inheritdoc}
      */