fuse: delete inode on drop

When inode is dropped (no more references) delete it from cache.

There's not much point in keeping it cached, when a new lookup will refresh
the attributes anyway.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>