Remove the dependency on cosmossdk.io/simapp

[damiannolan]

Summary

Our go module currently depends on cosmossdk.io/simapp. This module is pre-release and encapsulates the SDK's simulation app. We have no need to depend on this directly.

go mod why -m cosmossdk.io/simapp

# cosmossdk.io/simapp
github.com/cosmos/ibc-go/v7/testing/simapp/simd/cmd
cosmossdk.io/simapp/simd/cmd

We use the module to simply bootstrap the testnet subcommand of the ibc-go simapp. The testnet cmd can be redefined internally similarly to how prod apps do it. Alternatively we can remove this entirely if we don't see a need for the testnet subcommand.

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[DimitrisJim]

wdyt should be done here? Is this something we use/will use?

[damiannolan]

I think we can remove it and add it back later if its deemed necessary. I can make a quick PR