[EDELIVERY-15436] Removes note about self sending production ready

💬 Description

Self sending is production ready since 5.1. Removed the note and the message_id restrictions.

🔢 Affected Versions

These changes should be propagated to all 5.1 releases and 5.2 development.

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✅ Author's Check List

Before creating your MR, check:

• Your branch name, commit messages, MR Title
• Your Description is helpful/edited.
• All affected versions are indicated.

For your convenience:

MR Conventions	Example / Your MR
Branch Name Rule: Follows the pattern ^\bEDELIVERY-\b\b\d{5,}\b$	Example: EDELIVERY-13177 This MRs Source branch is: %{source_branch}.
Title Rule: Starts with \bEDELIVERY-\b\b\d{5,}\s	Example: EDELIVERY-13177 Updates S3 Configuration
Commit Messages Rule: Start with the pattern [EDELIVERY-	Example: [EDELIVERY-13477] Adds new auth properties re S3 This MRs first commit is: %{first_commit}

🤔 Questions?

See 📙 Updating eDelivery Documentation.

/cc @draguio @baciuco @rihtajo @tincuse @gautifr @maierga @breazio @durlaio @furcalu @azhikso @perpeio @venugar @ghouiah @bozmiha @monhaso @vedutvl