If we revoke a grant option from some role X, but X still holds the option
via another grant, we should not recursively revoke the privilege from
role(s) Y that X had granted it to. This was supposedly fixed as one
aspect of commit 4b2dafcc0b, but I must not
have tested it, because in fact that code never worked: it forgot to shift
the grant-option bits back over when masking the bits being revoked.
Per bug #6728 from Daniel German. Back-patch to all active branches,
since this has been wrong since 8.0.
ff122d3268