scsi: ufs: Remove is_rpmb_wlun()

Commit edc0596c ("scsi: ufs: core: Stop clearing UNIT ATTENTIONS")
removed all callers of is_rpmb_wlun(). Hence also remove the function
itself.

Link: https://lore.kernel.org/r/20211203231950.193369-4-bvanassche@acm.org


Reported-by: kernel test robot <lkp@intel.com>
Tested-by: Bean Huo <beanhuo@micron.com>
Reviewed-by: Asutosh Das <asutoshd@codeaurora.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Reviewed-by: Bean Huo <beanhuo@micron.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>