Remove unused MD5 generation logic for InsecureKey

What does this MR do and why?

• Contributes to #336421 (closed)
• Follow-up for: !66371 (merged)

Problem

FIPS environments don't support MD5 generation keys. Moreover, this code is not used anymore.

Solution

Remove unused MD5 generation logic

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.