USB: Follow-up to SPDX identifiers addition - remove now useless comments

USB: Follow-up to SPDX identifiers addition - remove now useless comments

All these files have been updated in the commit given in the Fixes: tag
below.

When the SPDX-License-Identifier: has been added, the corresponding text at
the beginning of the files has not been deleted.
All these texts are about GPL-2.0, with different variation in the wording.

Remove these now useless lines to save some LoC.

Fixes: e4858e309b9b ("USB: add SPDX identifiers to all remaining files in drivers/usb/")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>