cgroup: net: remove left over MODULE_LICENSE tag

The Kconfig currently controlling compilation of this code is:

net/Kconfig:config CGROUP_NET_PRIO
net/Kconfig:    bool "Network priority cgroup"

...meaning that it currently is not being built as a module by anyone,
as module support was discontinued in 2014.

We delete the MODULE_LICENSE tag since all that information is already
contained at the top of the file in the comments.

We don't delete module.h from the includes since it was no longer there
to begin with.

Cc: "David S. Miller" <davem@davemloft.net>
Cc: Tejun Heo <tj@kernel.org>
Cc: "Rosen, Rami" <rami.rosen@intel.com>
Cc: Daniel Wagner <daniel.wagner@bmw-carit.de>
Cc: netdev@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>