Fix sync protocol `next_sync_committee_branch` verification and remove active header#2829

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hwwhww wants to merge 2 commits intodevfrom

remove-active-header

Commits on Feb 10, 2022

`next_sync_committee_branch` validation bugfix and remove "active header"
hwwhww
committed
`next_sync_committee_branch` does not have to be empty
hwwhww
committed