staging: gdm724x: remove redundant license information

Now that the SPDX tag is in all gdm724x files, that identifies the
license in a specific and legally-defined manner.  So the extra GPL text
wording can be removed as it is no longer needed at all.

This is done on a quest to remove the 700+ different ways that files in
the kernel describe the GPL license text.  And there's unneeded stuff
like the address (sometimes incorrect) for the FSF which is never
needed.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>