Fix incorrect flip for graphic segments.

For some obscure reason, the end points of segments were swapped.
Note graphic RECTANGLE shapes have still an issue when flipped, but this
is a very different issue.
From master branch

common/eda_shape.cpp

@@ -401,8 +401,6 @@ void EDA_SHAPE::flip( const VECTOR2I& aCentre, bool aFlipLeftRight )
             m_start.y = aCentre.y - ( m_start.y - aCentre.y );
             m_end.y   = aCentre.y - ( m_end.y - aCentre.y );
         }
-
-        std::swap( m_start, m_end );
         break;
 
     case SHAPE_T::CIRCLE: