bug in aggregateVote.numAggregateSig

[djrtwo]

Issue

aggregateVote.numAggregateSig currently incorrectly uses the length of aggregate_sig to get the number of aggregate signatures.
https://github.com/ChainSafeSystems/lodestar_chain/blob/a270c7a577a3deda88f96cebb41bc3f173e26b1d/lodestar_chain/state/aggregateVote.js#L36-L38

aggregate_sig is in fact always just the length of 2 so this fails.

Proposed Implementation

You can use the number of 1s in the bitfield to get the length. If you need the length often, you might consider some sort of helper attribute that caches this results.

[djrtwo]

I'm not 100% sure what aggregateVote is being used for. Maybe it is just a relic of a previous version of the spec.

That said, this logic around BLS aggregate signatures still holds when used in other data structures.

[Mikerah]

Hi Danny,

Thank you so much for submitting an issue. We do indeed have relics of the previous spec in this repo. We are going to be going over the repo, and creating issues to make sure I follow your advice on making it easier for others to contribute.

[GregTheGreek]

I think this can be closed due to #39