Remove incorrect comment

This comment is stating that the code is adding a tab key, but it is not.

Author: Chekote

src/Selenium2Driver.php

@@ -689,8 +689,6 @@ public function setValue($xpath, $value)
 
         if (in_array($elementName, array('input', 'textarea'))) {
             $existingValueLength = strlen($element->attribute('value'));
-            // Add the TAB key to ensure we unfocus the field as browsers are triggering the change event only
-            // after leaving the field.
             $value = str_repeat(Key::BACKSPACE . Key::DELETE, $existingValueLength) . $value;
         }