The ownable upgradable modifier was not used anywhere
in the contract. The erc20 factory does not follow that
pattern. This change simplifies things by moving
values to immutables instead of being in storage.

This is a cleanup PR before migrating these contracts to
`contracts-bedrock`.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>