refactor(occlusion_spot): remove unused functions and refactor utils

[taikitanaka3]

Description

• refactor change

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[codecov]

Codecov Report

Merging #1628 (23960d8) into main (9ef82dc) will increase coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1628      +/-   ##
==========================================
+ Coverage   10.78%   10.80%   +0.02%     
==========================================
  Files        1109     1109              
  Lines       78426    78831     +405     
  Branches    18521    18769     +248     
==========================================
+ Hits         8457     8517      +60     
- Misses      61114    61438     +324     
- Partials     8855     8876      +21     

Flag	Coverage Δ		*Carryforward flag
differential	4.23% <0.00%> (?)
total	10.76% <0.00%> (ø)		Carriedforward from 096c395

*This pull request uses carry forward flags. Click here to find out more.

Impacted Files	Coverage Δ
...include/scene_module/occlusion_spot/grid_utils.hpp	0.00% <ø> (ø)
...ene_module/occlusion_spot/occlusion_spot_utils.hpp	57.14% <ø> (ø)
...ner/src/scene_module/occlusion_spot/grid_utils.cpp	0.00% <ø> (ø)
...ene_module/occlusion_spot/occlusion_spot_utils.cpp	13.11% <ø> (+3.11%)	⬆️
..._module/occlusion_spot/risk_predictive_braking.cpp	60.37% <ø> (+11.48%)	⬆️
...behavior_velocity_planner/src/utilization/util.cpp	20.47% <0.00%> (+3.62%)	⬆️
..._planner/test/src/test_risk_predictive_braking.cpp	67.56% <ø> (ø)
...ocity_planner/src/scene_module/run_out/manager.cpp	0.00% <0.00%> (ø)
...nner/src/scene_module/run_out/dynamic_obstacle.cpp	0.00% <0.00%> (ø)
... and 5 more

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[kyoichi-sugahara]

LGTM