drbd: Remove unused extern declarations

Commit b411b363 ("The DRBD driver") declared but never implemented
drbd_read_remote(), is_valid_ar_handle() and drbd_set_recv_tcq().
And commit 668700b4 ("drbd: Create a dedicated workqueue for sending acks on the control connection")
never implemented drbd_send_ping_wf().

Commit 2451fc3b ("drbd: Removed the BIO_RW_BARRIER support form the receiver/epoch code")
leave w_e_reissue() declaration unused.

Commit 8fe60551 ("drbd: Rename drbdd_init() -> drbd_receiver()")
rename drbdd_init() and leave unsued declaration. Also drbd_asender() is removed in
commit 1c03e520 ("drbd: Rename asender to ack_receiver").

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20240802095147.2788218-1-yuehaibing@huawei.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>