[18.4] Uninstall rexml 3.4.0 and ensure 3.4.4 is used

What does this MR do and why?

This backports !8811 (merged) to 18-4-stable.

Uninstall rexml 3.4.0 and ensure 3.4.4 is used. gitlab!210395 (merged) ensures that GitLab uses 3.4.4 instead of 3.4.2.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The original MR has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).

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