Some of the inputs to some functions in the Altair validator guide
were required in earlier iterations of the aggregation scheme but are
no longer required in the current version. This commit cleans up these
functions.
The sub-index calculation was incorrect when demonstrating how to map a validator in the sync committee to a particular bit in the `aggregation_bits` in the sync committee aggregation scheme. The correct index is given in this commit.
The field name `aggregation_bits` was changed from `aggregate_bits` to reflect the same usage under the attestation scheme. This PR cleans up left-over references to the old field name in the section header and TOC.