Investigate genesis pledge mismatch

**Issue summary**
While working on the https://github.com/ChainSafe/forest/pull/2910 we discovered that there's a mismatch in the genesis pledge.

https://github.com/ChainSafe/forest/blob/171ef54d15aca25c9dc22ac51a604d20fda83191/blockchain/state_manager/src/vm_circ_supply.rs#L42

In the Forest implementation, it's hard-coded to 0, while in [Lotus](https://github.com/filecoin-project/lotus/blob/06946a8fce1fbdb793c247ab6376676c0a96a2c9/chain/stmgr/supply.go#L59-L65) it follows a bit more sophisticated logic with a call to the [Power actor](https://github.com/filecoin-project/lotus/blob/06946a8fce1fbdb793c247ab6376676c0a96a2c9/chain/stmgr/supply.go#L294-L306).

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.

**Other information and links**

Start in blockchain/state_manager/src/vm_circ_supply.rs at the genesis pledge logic and compare it with the linked Lotus supply and Power actor code. Trace whether the value is used elsewhere in Forest, then determine whether aligning the calculation or removing the unused value is appropriate. Done means the mismatch is resolved or its intentional retention/removal is clearly established.

Written by the indexing model from the issue text.