btrfs: cleanup, remove inode_item_info helper

It's only a simple wrapper around btrfs_find_item, the locally defined
key is not used.

Signed-off-by: David Sterba <dsterba@suse.cz>

diff --cc fs/btrfs/backref.c
Simple merge

diff --cc fs/btrfs/backref.h
Simple merge

diff --cc fs/btrfs/scrub.c
Simple merge