chore: cleanup MLSCallHelper class (WPB-7153)

[ohassine]

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PR Submission Checklist for internal contributors

• The PR Title

  • conforms to the style of semantic commits messages¹ supported in Wire's Github Workflow²
  • contains a reference JIRA issue number like SQPIT-764
  • answers the question: If merged, this PR will: ... ³

• The PR Description

  • is free of optional paragraphs and you have filled the relevant parts to the best of your ability

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What's new in this PR?

Issues

• Renamed MLSCallHelper to CallHelper as it's used also for Proteus.
• Update documentation

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Testing

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PR Post Submission Checklist for internal contributors (Optional)

• Wire's Github Workflow has automatically linked the PR to a JIRA issue

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PR Post Merge Checklist for internal contributors

• If any soft of configuration variable was introduced by this PR, it has been added to the relevant documents and the CI jobs have been updated.

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References

1. https://sparkbox.com/foundry/semantic_commit_messages
2. https://github.com/wireapp/.github#usage
3. E.g. feat(conversation-list): Sort conversations by most emojis in the title #SQPIT-764.

[github-actions]

Test Results

3 054 tests   2 947 ✔️  3m 3s ⏱️
   523 suites     107 💤
   523 files           0 ❌

Results for commit 57925f4.

♻️ This comment has been updated with latest results.

[datadog-wireapp]

Datadog Report

All test runs 831f7f4 🔗

✅ 2 Total Test Services: 0 Failed, 2 Passed

Test Services

Service Name	Failed	Known Flaky	New Flaky	Passed	Skipped	Total Time	Test Service View
kalium-ios	0	0	0	2799	123	1.28s	Link
kalium-jvm	0	0	0	2947	107	7.2s	Link

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud