Remove not implemented session test

I have no clue what should be tested here and we anyway start session in
testsuite bootstrap.

Signed-off-by: Michal Čihař <michal@cihar.com>

test/Environment_test.php

@@ -68,17 +68,5 @@ class Environment_Test extends PHPUnit_Framework_TestCase
         );
         $this->assertEquals(5, $version_parts[1]);
     }
-
-    /**
-     * Test of session handling
-     *
-     * @return void
-     *
-     * @todo Think about this test
-     */
-    public function testSession()
-    {
-        $this->markTestIncomplete('No session testing');
-    }
 }
 ?>