btrfs: remove stale prototype of btrfs_write_inode

This function no longer exists, was removed in 3c427693 ("Btrfs: fix
btrfs_write_inode vs delayed iput deadlock").
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -3414,7 +3414,6 @@ void btrfs_split_delalloc_extent(struct inode *inode,
 void btrfs_set_range_writeback(struct btrfs_inode *inode, u64 start, u64 end);
 vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf);
 void btrfs_evict_inode(struct inode *inode);
-int btrfs_write_inode(struct inode *inode, struct writeback_control *wbc);
 struct inode *btrfs_alloc_inode(struct super_block *sb);
 void btrfs_destroy_inode(struct inode *inode);
 void btrfs_free_inode(struct inode *inode);