remove unused state_ field (backport #215)

[mergify]

The state_ field is not used.

---

This is an automatic backport of pull request #215 done by Mergify.

[mergify]

Cherry-pick of cb3a297 has failed:

On branch mergify/bp/humble/pr-215
Your branch is up to date with 'origin/humble'.

You are currently cherry-picking commit cb3a297.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   include/realtime_tools/realtime_server_goal_handle.hpp

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.73%. Comparing base (e263ce8) to head (7a97552).

Additional details and impacted files

@@           Coverage Diff           @@
##           humble     #218   +/-   ##
=======================================
  Coverage   76.73%   76.73%           
=======================================
  Files           8        8           
  Lines         460      460           
  Branches      175      175           
=======================================
  Hits          353      353           
  Misses         70       70           
  Partials       37       37           

Flag	Coverage Δ
unittests	76.73% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...clude/realtime_tools/realtime_server_goal_handle.h	78.26% <ø> (ø)