[HNSW] Only use dynamic max connections during tombstone cleanup

[trengrj]

What's being changed:

• Improved cleaning of tombstones #4003 improved tombstone cleanup performance but had a change to the initial select neighbors heuristic for HNSW which should use M rather than the dynamic M_max (which is double at layer 0). This change reverts that change while still leaving tombstone cleanups with the larger value to improve recall.

Review checklist

• Documentation has been updated, if necessary. Link to changed documentation:
• Chaos pipeline run or not necessary. Link to pipeline:
• All new code is covered by tests where it is reasonable.
• Performance tests have been run or not necessary.

[sonarcloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[weaviate-git-bot]

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