Remove Router/Processor Code (#4002)

## Issue Addressed

#3938 

## Proposed Changes

- `network::Processor` is deleted and all it's logic is moved to `network::Router`.
- The `network::Router` module is moved to a single file.
- The following functions are deleted: `on_disconnect` `send_status` `on_status_response` `on_blocks_by_root_request` `on_lightclient_bootstrap` `on_blocks_by_range_request` `on_block_gossip` `on_unaggregated_attestation_gossip` `on_aggregated_attestation_gossip` `on_voluntary_exit_gossip` `on_proposer_slashing_gossip` `on_attester_slashing_gossip` `on_sync_committee_signature_gossip` `on_sync_committee_contribution_gossip` `on_light_client_finality_update_gossip` `on_light_client_optimistic_update_gossip`. This deletions are possible because the updated `Router` allows the underlying methods to be called directly.

Author: danielrachi1