Remove unused dependency from online_signal_smoothing cmake

[tylerjw]

Description

This fixes this error:

CMake Error at online_signal_smoothing/CMakeLists.txt:49 (find_package):
  By not providing "Findros_testing.cmake" in CMAKE_MODULE_PATH this project
  has asked CMake to find a package configuration file provided by
  "ros_testing", but CMake did not find one.

  Could not find a package configuration file provided by "ros_testing" with
  any of the following names:

    ros_testingConfig.cmake
    ros_testing-config.cmake

  Add the installation prefix of "ros_testing" to CMAKE_PREFIX_PATH or set
  "ros_testing_DIR" to a directory containing one of the above files.  If
  "ros_testing" provides a separate development package or SDK, be sure it
  has been installed.

[vatanaksoytezer]

Should we add this to online_signal_smoothing instead

[tylerjw]

Should we add this to online_signal_smoothing instead

online_signal_smoothing is just a subdirectory of moveit_core.

[codecov]

Codecov Report

Merging #839 (7ef503d) into main (595813c) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #839      +/-   ##
==========================================
+ Coverage   57.79%   57.79%   +0.01%     
==========================================
  Files         305      305              
  Lines       26060    26060              
==========================================
+ Hits        15059    15060       +1     
+ Misses      11001    11000       -1     

Impacted Files	Coverage Δ
...nning_scene_monitor/src/planning_scene_monitor.cpp	53.31% <0.00%> (+0.12%)	⬆️

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[tylerjw]

I found this when working on #842