netfilter: Remove the now superfluous sentinel elements from ctl_table array

netfilter: Remove the now superfluous sentinel elements from ctl_table array

This commit comes at the tail end of a greater effort to remove the
empty elements at the end of the ctl_table arrays (sentinels) which will
reduce the overall build time size of the kernel and run time memory
bloat by ~64 bytes per sentinel (further information Link :
https://lore.kernel.org/all/ZO5Yx5JFogGi%2FcBo@bombadil.infradead.org/)

* Remove sentinel elements from ctl_table structs
* Remove instances where an array element is zeroed out to make it look
  like a sentinel. This is not longer needed and is safe after commit
  c899710fe7f9 ("networking: Update to register_net_sysctl_sz") added
  the array size to the ctl_table registration
* Remove the need for having __NF_SYSCTL_CT_LAST_SYSCTL as the
  sysctl array size is now in NF_SYSCTL_CT_LAST_SYSCTL
* Remove extra element in ctl_table arrays declarations

Acked-by: Kees Cook <keescook@chromium.org> # loadpin & yama
Signed-off-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>