scsi: target: Remove the unused function transport_lba_64_ext()

The function transport_lba_64_ext() is defined in the target_core_sbc.c
file, but not called elsewhere, so remove this unused function.

drivers/target/target_core_sbc.c:276:34: warning: unused function 'transport_lba_64_ext'.

Link: https://bugzilla.openanolis.cn/show_bug.cgi?id=2427
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221018081235.124662-1-jiapeng.chong@linux.alibaba.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>