sched/deadline: remove unused dl_bandwidth

The default deadline bandwidth control structure has been removed since
commit eb77cf1c ("sched/deadline: Remove unused def_dl_bandwidth")
leading to unused init_dl_bandwidth() and struct dl_bandwidth. Remove
them to clean up the code.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20230524102514.407486-1-linmiaohe@huawei.com