fix: mockExecutionEngine without checking parentHash

[yrong]

Motivation

Start the beacon node in mock mode without requiring an execution node.

Description

#6188

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #6323 (2034ecd) into unstable (551fd8e) will not change coverage.
Report is 6 commits behind head on unstable.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff            @@
##           unstable    #6323   +/-   ##
=========================================
  Coverage     76.53%   76.53%           
=========================================
  Files           248      248           
  Lines         25943    25943           
  Branches       1449     1449           
=========================================
  Hits          19855    19855           
  Misses         6058     6058           
  Partials         30       30           

[nflaig]

We can't just remove those checks like this a we use the engine mock for testing as well.

I think the engine mock is useful for people that want to quickly spin up a node on any network and we should think about how we can make it so it does not report syncing unless the node is synced from genesis.

Since the engine mock is not secure either way as it does not validate the execution payloads I think removing the parent hash validation doesn't matter much but I would like to hear what others have to say about this.

I am in favor of removing this and for testing, we can explicitly configure the engine mock to do parent hash validation.