ArduCopter: remove check for max INS instances

For all supported boards the maximum number of instances is 3.

ArduCopter/motors.cpp

@@ -398,7 +398,6 @@ bool Copter::pre_arm_checks(bool display_failure)
             return false;
         }
 
-#if INS_MAX_INSTANCES > 1
         // check all accelerometers point in roughly same direction
         if (ins.get_accel_count() > 1) {
             const Vector3f &prime_accel_vec = ins.get_accel();
@@ -423,7 +422,6 @@ bool Copter::pre_arm_checks(bool display_failure)
                 }
             }
         }
-#endif
 
         // check gyros are healthy
         if(!ins.get_gyro_health_all()) {
@@ -433,7 +431,6 @@ bool Copter::pre_arm_checks(bool display_failure)
             return false;
         }
 
-#if INS_MAX_INSTANCES > 1
         // check all gyros are consistent
         if (ins.get_gyro_count() > 1) {
             for(uint8_t i=0; i<ins.get_gyro_count(); i++) {
@@ -447,7 +444,6 @@ bool Copter::pre_arm_checks(bool display_failure)
                 }
             }
         }
-#endif
 
         // get ekf attitude (if bad, it's usually the gyro biases)
         if (!pre_arm_ekf_attitude_check()) {