chore(tm,solo): delete unused GetProofSpecs

[siburu]

Description

GetProofSpecs had been defined as a method of exported.ClientState, but was already removed from the interface.
This PR deletes implementations of GetProofSpecs, which still exist in the source code but aren't called from anywhere.

Commit Message / Changelog Entry

chore(tm,solo): delete unused GetProofSpecs

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[crodriguezvega]

Thanks for the cleanup, @siburu!