btrfs-progs: device: add description of alias to help message

State that the 'delete' is the alias of 'remove' as the man page says.

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

cmds-device.c

@@ -237,7 +237,7 @@ static int cmd_device_remove(int argc, char **argv)
 
 static const char * const cmd_device_delete_usage[] = {
 	"btrfs device delete <device>|<devid> [<device>|<devid>...] <path>",
-	"Remove a device from a filesystem",
+	"Remove a device from a filesystem (alias of \"btrfs device remove\")",
 	NULL
 };