btrfs: remove unused BTRFS_TOTAL_BYTES_PINNED_BATCH

This hasn't been used since 138a12d8 ("btrfs: rip out
btrfs_space_info::total_bytes_pinned") so it is safe to remove.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -92,14 +92,6 @@ struct reloc_control;
 
 #define BTRFS_DIRTY_METADATA_THRESH	SZ_32M
 
-/*
- * Use large batch size to reduce overhead of metadata updates.  On the reader
- * side, we only read it when we are close to ENOSPC and the read overhead is
- * mostly related to the number of CPUs, so it is OK to use arbitrary large
- * value here.
- */
-#define BTRFS_TOTAL_BYTES_PINNED_BATCH	SZ_128M
-
 #define BTRFS_MAX_EXTENT_SIZE SZ_128M
 
 /*