docs: Remove troubleshooting for Ruby 2.3 or earlier (and for openssl 1.0.2)

What does this Merge Request do and why?

Remove a legacy troubleshooting from Ruby as:

• it is mainly for Ruby 2.3 or earlier, which was at least EOL'ed in 2019-03
  • https://github.com/rbenv/ruby-build/issues/1353
• it is only for openssl 1.0.2, which was EOL'ed in 2019-12

Updates !125 (merged)

cf. omnibus-gitlab!3069 (merged) (%12.1)

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• [n/a] Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• [n/a] gdk doctor test added, if needed.
• [n/a] Add the ~highlight label if this MR should be included in the CHANGELOG.md.