nilfs2: remove own inode hash used for GC

This uses inode hash function that vfs provides instead of the own
hash table for caching gc inodes.  This finally removes the own inode
hash from nilfs.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

diff --cc fs/nilfs2/gcinode.c
Simple merge

diff --cc fs/nilfs2/inode.c
Simple merge

diff --cc fs/nilfs2/ioctl.c
Simple merge

diff --cc fs/nilfs2/nilfs.h
Simple merge

diff --cc fs/nilfs2/segment.c
Simple merge

diff --cc fs/nilfs2/the_nilfs.c
Simple merge

diff --cc fs/nilfs2/the_nilfs.h
Simple merge