fix: remove condition to allow 'cosmos' as valid value for verifyingContract field in typed signatures

[jpuri]

We have added code to allow cosmos as valid verifyingContract value for typed signatures. The reason for this is to keep support signature signing on cosmos network.

A lot of cosmos dapps use this deprecated sdk with hard coded value of verifyingContract: https://github.com/evmos/ethermint/blob/main/ethereum/eip712/domain.go#L29

Once users stop using this SDK we can remove this hard coded condition.

Ref: MetaMask/metamask-extension#26980

[legobeat]

Perhaps contract verification can be toggled/configured via a constructor parameter in a way that could make this transition non-breaking?