Reverts parts of #14779

If a split (which calls writeInitialState for the new range) straddles
an upgrade to a build which includes #14779, inconsistency could
result as only those replicas which processed the split before the
upgrade would have the frozen field present (and while the frozen
field could easily be ignored in the consistency checker, its impact
on the stats is tricker to back out). This commit reintroduces the
field by always writing a zero to it when creating a range.

Fixes #14891