Returns |(X - X2ᵀ)/lengthscales| (L2-norm).

def scaled_euclid_dist(self, X, X2):  # pragma: no cover
        """
        Returns |(X - X2ᵀ)/lengthscales| (L2-norm).
        """
        warnings.warn('scaled_euclid_dist is deprecated and will be removed '
                      'in GPflow version 1.4.0. For stationary kernels, '
                      'define K_r(r) instead.',
                      DeprecationWarning)
        r2 = self.scaled_square_dist(X, X2)
        return self._clipped_sqrt(r2)