Add -Wunused-function

[ChrisThrasher]

Description

This function is regarded as unused in some translation units because it's marked static but not used in every single TU where it's included. static free functions are typically only used within a single TU as a way to tell the compiler that no other TUs will link to this function.

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[tylerjw]

This is a nice little cleanup, thank you!

[codecov]

Codecov Report

Base: 50.95% // Head: 50.95% // Decreases project coverage by -0.01% ⚠️

Coverage data is based on head (af96196) compared to base (acc64da).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1754      +/-   ##
==========================================
- Coverage   50.95%   50.95%   -0.00%     
==========================================
  Files         378      378              
  Lines       31659    31671      +12     
==========================================
+ Hits        16130    16136       +6     
- Misses      15529    15535       +6     

Impacted Files	Coverage Δ
...bullet/src/bullet_integration/ros_bullet_utils.cpp	65.00% <0.00%> (-27.85%)	⬇️
...nning_scene_monitor/src/planning_scene_monitor.cpp	45.21% <0.00%> (-0.43%)	⬇️
moveit_ros/moveit_servo/src/pose_tracking.cpp	77.26% <0.00%> (+0.48%)	⬆️
moveit_ros/moveit_servo/src/servo_calcs.cpp	67.43% <0.00%> (+1.46%)	⬆️

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