staging: mt7621-pci: remove GPL2+ text from license header

This file has a valid SPDX license line added so reamining
GPL2+ boilerplate text is not needed at all. Remove it.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>