scsi: libsas: Remove temporarily-added _gfp() API variants

These variants were added for bisectability. Remove them, as all call sites
have now been convertd to use the original API.

Link: https://lore.kernel.org/r/20210118100955.1761652-20-a.darwish@linutronix.de
Cc: Jason Yan <yanaijie@huawei.com>
Reviewed-by: John Garry <john.garry@huawei.com>
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>