[meta] Remove Drupal\social_group\SocialGroupHelperService

Problem/Motivation

The SocialGroupHelperService is used as a dumping ground for all sorts of disjointed logic that should either be moved into a more well-defined and scoped service with a clear purpose but most likely should just be moved into the call-site of the function being called or into an entity (storage) or bundle class directly.

The "service" also currently uses direct database queries rather than the entity query API which can provide problems in case of storage changes or missing access checks.

Steps to reproduce

Proposed resolution

Evaluate the different functions in the service, deprecate and remove them as needed. We can deprecate the entire service already but it's unclear whether we can remove it before the 13.0.0 release. However we may already be able to remove some functions by that version.

We should split this up into separate child issues.

Merge request link

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet