Remove VULN_THRESHLD relic

[drwetter]

This fixes #2973.

There was a while back an extra headline when one or a defined other number of vulnerabilities were checked. The extra headline was removed n #2967 but some leftover code needed to be removed as well.

In the aforementioned previous PR it seems run_starttls_injection() and run_rc4() were forgotten. This PR removes extra headlines in those functions as well.

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• Bug fix
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• Breaking change (bug fix, feature or improvement that would cause existing functionality to not work as expected)
• Typo fix
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If it's a code change please check the boxes which are applicable

• For the main program: My edits contain no tabs, indentation is five spaces and any line endings do not contain any blank chars
• I've read CONTRIBUTING.md and Coding_Convention.md
• I have tested this fix or improvement against >=2 hosts and I couldn't spot a problem
• I have tested this new feature against >=2 hosts which show this feature and >=2 host which does not (in order to avoid side effects) . I couldn't spot a problem
• For the new feature I have made corresponding changes to the documentation and / or to help()
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