Remove Jenkins Agent for node18

[ElfenB]

Is your feature request related to a problem? Please describe.
Node.js 18 reached its end-of-life on April 30, 2025, meaning no more security updates or maintenance.

Describe the solution you'd like
Remove jenkins-agent-nodejs18

Describe alternatives you've considered
Not sure if it's possible to deprecate.

Additional context
Node.js Releases