net ipv4: Remove the unneeded registration of an empty net/ipv4/neigh

sysctl no longer requires explicit creation of directories.  The neigh
directory is always populated with at least a default entry so this
won't cause any user visible changes.

Delete the ipv4_path and the ipv4_skeleton these are no longer needed.

Directly register the ipv4_route_table.

And since I am an idiot remove the header definitions that I should
have removed in the previous patch.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Acked-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>