[fix](editlog) Remove dead editStream field and guaranteed-NPE getEditLogSize()

[dataroaring]

Summary

• The `editStream` field (`EditLogOutputStream`) is declared but never assigned anywhere — it is always `null`
• `getEditLogSize()` calls `editStream.length()`, which will always throw `NullPointerException`
• Remove both the unused field and the dead method

Test plan

• Verify FE compiles and starts normally
• Verify no code references `getEditLogSize()` (confirmed by grep)

🤖 Generated with Claude Code

[Thearas]

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[Copilot]

Pull request overview

Removes a dead editStream field and its associated getEditLogSize() method in EditLog, eliminating a guaranteed NullPointerException path and reducing unused API surface.

Changes:

• Deleted the never-assigned editStream field.
• Removed getEditLogSize() which dereferenced the null editStream.

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