btrfs: remove struct rcu_string

The only use for device name has been removed so we can kill the RCU
string API.

Reviewed-by: Daniel Vacek <neelx@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

fs/btrfs/rcu-string.h

@@ -18,7 +18,6 @@
 #include "transaction.h"
 #include "volumes.h"
 #include "raid56.h"
-#include "rcu-string.h"
 #include "dev-replace.h"
 #include "sysfs.h"
 #include "tree-checker.h"

fs/btrfs/volumes.c

@@ -21,7 +21,6 @@
 #include <uapi/linux/btrfs.h>
 #include <uapi/linux/btrfs_tree.h>
 #include "messages.h"
-#include "rcu-string.h"
 #include "extent-io-tree.h"
 
 struct block_device;

fs/btrfs/volumes.h

@@ -9,7 +9,6 @@
 #include "ctree.h"
 #include "volumes.h"
 #include "zoned.h"
-#include "rcu-string.h"
 #include "disk-io.h"
 #include "block-group.h"
 #include "dev-replace.h"