btrfs: transaction_kthread() is not freezable

transaction_kthread() is calling try_to_freeze(), but that's just an
expeinsive no-op given the fact that the thread is not marked freezable.

After removing this, disk-io.c is now independent on freezer API.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -25,7 +25,6 @@
 #include <linux/buffer_head.h>
 #include <linux/workqueue.h>
 #include <linux/kthread.h>
-#include <linux/freezer.h>
 #include <linux/slab.h>
 #include <linux/migrate.h>
 #include <linux/ratelimit.h>
@@ -1928,14 +1927,12 @@ static int transaction_kthread(void *arg)
 		if (unlikely(test_bit(BTRFS_FS_STATE_ERROR,
 				      &root->fs_info->fs_state)))
 			btrfs_cleanup_transaction(root);
-		if (!try_to_freeze()) {
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (!kthread_should_stop() &&
 				(!btrfs_transaction_blocked(root->fs_info) ||
 				 cannot_commit))
 			schedule_timeout(delay);
 		__set_current_state(TASK_RUNNING);
-		}
 	} while (!kthread_should_stop());
 	return 0;
 }