Remove RBFPID::ToString

- This cause build error on some environment, "#include <iostream>" is trouble maker but, IDK why??

inc/rbfpid.h

@@ -3,9 +3,6 @@
 
 #include "../Eigen/Dense"
 
-#include <string>
-#include <iostream>
-
 namespace RbfpidBalbot {
 namespace control {
 class RBFPID {
@@ -56,12 +53,6 @@ class RBFPID {
    * @return double output (input of plant)
    */
   double Update(double e, double y);
-
-  std::string ToString() {
-       std::ostringstream ss;
-       ss << "kp " << kp_ << " ki " << ki_ << " kd " << kd_;
-       return ss.str();
-  }
 };
 };  // namespace control
 };  // namespace RbfpidBalbot

src/app_main.cpp

@@ -66,7 +66,7 @@ void AppMain(void) {
     uf = (u / u_motor_factor); //+ (u >= 0 ? 0.3 : -0.3);
     hardware::SetMotor(false, uf);
     if (i % 100 == 0) {
-      LOG_INF("e %6f u %6f uf %6f %s", -euler[0], u, uf, pid.ToString().c_str());
+      LOG_INF("e %6f u %6f uf %6f", -euler[0], u, uf);
       gpio_pin_toggle_dt(&hardware::run_led);
       //LOG_INF("q %f %f %f %f", quad[0], quad[1], quad[2], quad[3]);
     }