fix(dropAndReplace): use dummy signature in drop and replace

[moldy530]

Pull Request Checklist

• Did you add new tests and confirm existing tests pass? (yarn test)
• Did you update relevant docs? (docs are found in the site folder, and guidelines for updating/adding docs can be found in the contribution guide)
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PR-Codex overview

The focus of this PR is to update the signature handling in the dropAndReplaceUserOperation function by replacing it with account.getDummySignature().

Detailed summary

• Updated signature handling in dropAndReplaceUserOperation function
• Replaced signature with await account.getDummySignature()

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