Remove service_name from TaskExecutor

[ackintosh]

Description

The service_name field is no longer used since we integrated tracing and reconstructed spans, so I think it can be safely removed.

Previously, the service name was included in the logger output, for example:

Apr 05 07:03:07.646 DEBUG Sync's view on execution engine state updated  past_state: Online, new_state: Offline, service: "sync"

Currently, the service field is missing from the logs. However, similar contextual information can be obtained by using the --log-extra-info flag, which produces logs like the following:

Dec 16 06:38:32.054 DEBUG network::sync::network_context::beacon_node/network/src/sync/network_context.rs:1292 Sync's view on execution engine state updated  past_state: Online, new_state: Online

Given this, the service_name field no longer seems necessary.

[akronim26]

Working on this!