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>

include/target/target_core_base.h

@@ -73,9 +73,8 @@
 /*
  * struct se_device->dev_flags
  */
-#define DF_READ_ONLY				0x00000001
-#define DF_SPC2_RESERVATIONS			0x00000002
-#define DF_SPC2_RESERVATIONS_WITH_ISID		0x00000004
+#define DF_SPC2_RESERVATIONS			0x00000001
+#define DF_SPC2_RESERVATIONS_WITH_ISID		0x00000002
 
 /* struct se_dev_attrib sanity values */
 /* Default max_unmap_lba_count */