Investigate genesis pledge mismatch

[LesnyRumcajs]

Issue summary
While working on the #2910 we discovered that there's a mismatch in the genesis pledge.

forest/blockchain/state_manager/src/vm_circ_supply.rs

Line 42 in 171ef54

genesis_pledge: TokenAmount,

In the Forest implementation, it's hard-coded to 0, while in Lotus it follows a bit more sophisticated logic with a call to the Power actor.

This, in turn, leaves Forest with 0 for the genesis pledge and Lotus with 2 attoFIL. It doesn't appear to be consensus-critical but may surface in the future, and it would be good to align with the Lotus implementation. Otherwise, we should consider removing it if it's not used at all.

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