bcachefs: Kill writing old accounting to journal

bcachefs: Kill writing old accounting to journal

More ripping out of the old disk space accounting.

Note that the new disk space accounting is incompatible with the old,
and writing out old style disk space accounting with the new code is
infeasible.

This means upgrading and downgrading past this version requires
regenerating accounting.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>