chore(edit-sync): drop the stale mutation counts from the supersedesIdentity comment

[mtskf]

Summary

The supersedesIdentity comment in src/webview/cm/edit-sync.ts cited how many tests go red when from/to is swapped, and the figure for the shouldDropBufferedForEpoch side was out of date. This rewrites the sentence so it no longer depends on a count.

Changes

• Comment only — no code or test changes.
• Re-measured: swapping the arguments in shouldDropBufferedForEpoch and running pnpm vitest run reds 22 tests across three files (13 in cm-edit-sync.test.ts, 4 in editor.test.ts, 5 in shell.test.ts), not the "5 + 2" the comment claimed.
• Since any count drifts as tests are added, the comment now names the three test files that hold the direction and keeps the "do not delete them in a tidy-up" warning.

Related

• TODO: edit-sync.ts の supersedesIdentity コメントの mutation 件数を実測値に直す (found in the PR chore(protocol): require the Document epoch identity pair #429 review cycle)

Test Plan

• Swap applied (asserted non-no-op), measured, then restored — the diff is the comment alone
• pnpm compile, lint and pnpm vitest run green on the final tree