Fix extrusion rate smoothing unnecessarily slowing down the entire line (#11249)

* Fix typo & code style

* Fix calculation of the min acc time

* Avoid slowing down the entire line if both end of a single line has been slowed down

src/libslic3r/GCode/PressureEqualizer.hpp

@@ -136,7 +136,6 @@ private:
             assert(avg_correction <= 1.00000001f);
             return avg_correction;
         }
-        float       time_corrected()  const { return time() * volumetric_correction_avg(); }
 
         GCodeLineType type;