scsi: target: Remove unused declarations

Commit 13247018 ("scsi: target: iscsi: Fix hang in the iSCSI login
code") removed iscsi_handle_login_thread_timeout() but left declaration.

Commit 3e1c81a9 ("iscsi-target: Refactor RX PDU logic + export request
PDU handling") left iscsi_target_get_initial_payload() declaration.

Commit d703ce2f ("iscsi/iser-target: Convert to command priv_size
usage") remove iscsit_alloc_cmd() but left declaration.

And finally, a few other declarations were never implenmented since
introduction in commit e48354ce ("iscsi-target: Add iSCSI fabric
support for target v4.1").

Signed-off-by: Yue Haibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20240810093437.2586476-1-yuehaibing@huawei.com


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>