remove unused scipy dependency missing from latest version

roboticstoolbox/mobile/EKF.py

@@ -3,10 +3,11 @@
 @Author: Peter Corke, original MATLAB code and Python version
 @Author: Kristian Gibson, initial MATLAB port
 """
+
 from collections import namedtuple
 import numpy as np
 from math import pi
-from scipy import integrate, randn
+from scipy import integrate
 from scipy.linalg import sqrtm, block_diag
 from scipy.stats.distributions import chi2
 import matplotlib.pyplot as plt