[Process] Remove a misleading comment

The described behaviour was never implemented.

Author: jakzal

src/Symfony/Component/Process/Process.php

@@ -201,9 +201,6 @@ public function run($callback = null)
      * The callback receives the type of output (out or err) and some bytes from
      * the output in real-time while writing the standard input to the process.
      * It allows to have feedback from the independent process during execution.
-     * If there is no callback passed, the wait() method can be called
-     * with true as a second parameter then the callback will get all data occurred
-     * in (and since) the start call.
      *
      * @param callback|null $callback A PHP callback to run whenever there is some
      *                                output available on STDOUT or STDERR