Remove check for eventmachine gem

What does this Merge Request do and why?

When the thin gem was removed from gitlab: gitlab!89258 (merged), it also removed eventmachine gem.

This causes gdk doctor to fail about eventmachine because it's not installed. This MR removed the check so gdk doctor can pass.

CC @jay_mccure

Merge Request checklist

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