nilfs2: allow nilfs_destroy_inode to destroy metadata file inodes

The current nilfs_destroy_inode() doesn't handle metadata file inodes
including gc inodes (dummy inodes used for garbage collection).

This allows nilfs_destroy_inode() to destroy inodes of metadata files.

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

fs/nilfs2/mdt.c

@@ -577,7 +577,5 @@ void nilfs_mdt_destroy(struct inode *inode)
 		nilfs_palloc_destroy_cache(inode);
 	nilfs_mdt_clear(inode);
 
-	kfree(mdi->mi_bgl); /* kfree(NULL) is safe */
-	kfree(mdi);
 	nilfs_destroy_inode(inode);
 }