pcbnew: Don't refresh S_CURVE in bbox()

The bounding box calculation needs to be fast and is threaded in many
places in pcbnew.  We cannot invalidate items (the function is const but
this wasn't caught at compile-time for some reason) when getting the
bbox. This shouldn't be an issue as the m_BezierPoints is rebuilt each
time the curve is updated, so rebuilding during the bbox seems extra.

Fixes: lp:1819984
* https://bugs.launchpad.net/kicad/+bug/1819984

pcbnew/class_drawsegment.cpp

@@ -557,8 +557,6 @@ const EDA_RECT DRAWSEGMENT::GetBoundingBox() const
 	}
 
     case S_CURVE:
-        // Rebuild the poly points shape
-        ((DRAWSEGMENT*)this)->RebuildBezierToSegmentsPointsList( m_Width );
 
         for( unsigned ii = 0; ii < m_BezierPoints.size(); ++ii )
             bbox.Merge( m_BezierPoints[ii] );