affs: remove useless superblock writeout on unmount

We do not need to write out the superblock from '->put_super()' because VFS has
already called '->sync_fs()' by this time and the superblock has already been
written out. Thus, remove the 'affs_commit_super()' infocation from
'affs_put_super()'.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>