More typos fixes in sharding

[ericsson49]

Fixed typos in the methods:

• process_shard_header:
  • body_summary missed when accessingShardBlobBodySummary.beacon_block_root
• process_pending_headers
  • c variable name used instead of header
• charge_confirmed_header_fees:
  • get_shard_proposer used instead of get_shard_proposer_index
• reset_pending_headers
  • SLOTS_IN_EPOCH used instead of SLOTS_PER_EPOCH
  • state missed in get_committee_count_per_slot(next_epoch) call
• process_epoch
  • process_confirmed_header_fees called instead of charge_confirmed_header_fees

[protolambda]

Thank you! We will make this part of the spec executable in a week or two, and run some tests and linting, to try and catch things like this.