Only send a single sync committee signature per validator

[dapplion]

Motivation

If a validator is assigned multiple sync committee indexes they will sign and send multiple sync committee signatures. This is unnecessary and will cause a ton of errors in the beacon node side.

Eph 3/6 1.644 [API]             error: Error on publishContributionAndProofs [12] slot=101, subCommitteeIndex=2 code=SYNC_COMMITTEE_ERROR_NOT_CURRENT_SLOT, currentSlot=102, slot=101                                                                                           Error: SYNC_COMMITTEE_ERROR_NOT_CURRENT_SLOT                                                                                                at validateGossipSyncCommitteeExceptSig (/home/cayman/Code/lodestar/packages/lodestar/src/chain/validation/syncCommittee.ts:85:11)      at validateSyncCommitteeGossipContributionAndProof (/home/cayman/Code/lodestar/packages/lodestar/src/chain/validation/syncCommitteeC
ontributionAndProof.ts:30:3)                                                                                                            
    at map (/home/cayman/Code/lodestar/packages/lodestar/src/api/impl/validator/index.ts:370:19)                                        
    at Array.map (<anonymous>)                                                                                                          
    at Object.publishContributionAndProofs (/home/cayman/Code/lodestar/packages/lodestar/src/api/impl/validator/index.ts:367:31)        
    at Object.handler (/home/cayman/Code/lodestar/packages/api/src/server/utils/server.ts:70:29)                                        
    at preHandlerCallback (/home/cayman/Code/lodestar/node_modules/fastify/lib/handleRequest.js:124:28)                                 
    at preValidationCallback (/home/cayman/Code/lodestar/node_modules/fastify/lib/handleRequest.js:107:5)                                   at handler (/home/cayman/Code/lodestar/node_modules/fastify/lib/handleRequest.js:70:7)                                              
    at done (/home/cayman/Code/lodestar/node_modules/fastify/lib/contentTypeParser.js:151:7) 

Description

• Sign and send a single sync committee signature per validator.
• Update the types to make this easier to track manage.
• Change the data ordering the sync committee nested Maps data structure to make pruning easier

[codeclimate]

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