docs(accel_brake_map_calibrator): add parameter descriptions

[TakaHoribe]

Description

• Add parameter description in the readme
• remove unused parameter

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[tkimura4]

LGTM

[codecov]

Codecov Report

Base: 10.34% // Head: 10.30% // Decreases project coverage by -0.03% ⚠️

Coverage data is based on head (de6bc8f) compared to base (a63ed16).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1918      +/-   ##
==========================================
- Coverage   10.34%   10.30%   -0.04%     
==========================================
  Files        1146     1146              
  Lines       81464    81780     +316     
  Branches    19003    19003              
==========================================
  Hits         8429     8429              
- Misses      63915    64231     +316     
  Partials     9120     9120              

Flag	Coverage Δ		*Carryforward flag
differential	0.00% <ø> (?)
total	10.32% <ø> (ø)		Carriedforward from a63ed16

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

Impacted Files	Coverage Δ
...map_calibrator/accel_brake_map_calibrator_node.hpp	0.00% <ø> (ø)
...calibrator/src/accel_brake_map_calibrator_node.cpp	0.00% <ø> (ø)

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