target: Remove obsolete DF_READ_ONLY usage

This was used at one time as a hack by FILEIO backend registration to
allow a struct block_device that was claimed with blkdev_get (by a local
filesystem mount for example) to be exported as read-only (SCSI WP=1).

Since FILEIO backend registration will no longer attempt to obtain
exclusive access to an underlying struct block_device here, this flag is
now obsolete.

Reported-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/target/target_core_tpg.c b/drivers/target/target_core_tpg.c
index 70c3ffb..c672a40cb 100644
--- a/drivers/target/target_core_tpg.c
+++ b/drivers/target/target_core_tpg.c
@@ -175,10 +175,7 @@
 		 * demo_mode_write_protect is ON, or READ_ONLY;
 		 */
 		if (!tpg->se_tpg_tfo->tpg_check_demo_mode_write_protect(tpg)) {
-			if (dev->dev_flags & DF_READ_ONLY)
-				lun_access = TRANSPORT_LUNFLAGS_READ_ONLY;
-			else
-				lun_access = TRANSPORT_LUNFLAGS_READ_WRITE;
+			lun_access = TRANSPORT_LUNFLAGS_READ_WRITE;
 		} else {
 			/*
 			 * Allow only optical drives to issue R/W in default RO