[NET_SCHED]: kill obsolete NET_CLS_POLICE option

The code is already gone for about half a year, the config option
has been kept around to select the replacement options for easier
upgrades. This seems long enough, people upgrading from older
kernels will have to reconfigure a lot anyway.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>