locking implementation based Keybase implementation should be hidden

[alessio]

We should not export the New constructor of the crypto.Keybase old locking implementation-based dbKeybase. Most of the codebase has already been ported to LazyKeyBase, plus a NewInMemory constructor has already been made available to meet the in-memory keybase use case requirements.

cc @cosmos/cosmossdk

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[alessio]

It'd be great to include this in the future v0.32.0 release.