vfio-pci/zdev: Remove repeated verbose license text

vfio-pci/zdev: Remove repeated verbose license text

The SPDX and verbose license text are redundant, however in this case
the verbose license indicates a GPL v2 only while SPDX specifies v2+.
Remove the verbose license and correct SPDX to the more restricted
version.

Signed-off-by: Cai Huoqing <caihuoqing@baidu.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/r/20210824003749.1039-1-caihuoqing@baidu.com
[aw: commit log]
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>