ipv4: Remove old route notifications and convert listeners

Unlike mlxsw, the other listeners to the FIB notification chain do not
require any special modifications as they never considered multiple
identical routes.

This patch removes the old route notifications and converts all the
listeners to use the new replace / delete notifications.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>