Remove ci jobs for Iron irwini

[Yadunund]

Made changes similar to

• Remove all references to Galactic. #687
• Completely remove Foxy support. #717

[clalancette]

While I approve of this, I think we should hold off on merging this until we've had the final sync out for at least a month. That way, if we need to do another patch release for some reason, everything still exists. Thus I'm going to mark this as a "Draft" for right now, though I am going to manually disable the iron_coverage job on https://ci.ros2.org to save us a bit of compute time.

[Yadunund]

@cottsay / @nuclearsandwich this PR should be ready to merge after a quick review.

[j-rivero]

Good to my eyes.

grep is reporting a few more occurrences in linux_docker_resources, do we need to delete these too?

ci on  yadu/iron-eol underwent 10s❯ grep -R 'iron ' *
linux_docker_resources/Dockerfile-RHEL:    $(if test \( ${ROS_DISTRO} = humble -o ${ROS_DISTRO} = iron \); then echo tinyxml-devel; fi) \
linux_docker_resources/Dockerfile:    ; elif test \( ${ROS_DISTRO} = iron \); then \
linux_docker_resources/Dockerfile:RUN if test \( ${ROS_DISTRO} = humble -o ${ROS_DISTRO} = iron \); then apt-get update && apt-get install --no-install-recommends -y libtinyxml-dev; f

[Yadunund]

@j-rivero thanks for flagging those file! I've removed traces of Iron from those in fe9c14f.