fsnotify: Drop inode_mark.c

inode_mark.c now contains only a single function. Move it to
fs/notify/fsnotify.c and remove inode_mark.c.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>