DOC: Remove plots from docstring examples

Plotting isn't really necessary in a docstring example. Both of these functions already have gallery examples.

skimage/transform/finite_radon_transform.py

@@ -46,14 +46,6 @@ def frt2(a):
 
     >>> f = frt2(img)
 
-    Plot the results::
-
-        import matplotlib.pyplot as plt
-        plt.imshow(f, interpolation='nearest', cmap=plt.cm.gray)
-        plt.xlabel('Angle')
-        plt.ylabel('Translation')
-        plt.show()
-
     References
     ----------
     .. [FRT] A. Kingston and I. Svalbe, "Projective transforms on periodic

skimage/transform/hough_transform.py

@@ -131,14 +131,6 @@ def hough(img, theta=None):
 
     >>> out, angles, d = hough(img)
 
-    Plot the results::
-
-        import matplotlib.pyplot as plt
-        plt.imshow(out, cmap=plt.cm.bone)
-        plt.xlabel('Angle (degree)')
-        plt.ylabel('Distance %d (pixel)' % d[0])
-        plt.show()
-
     .. plot:: hough_tf.py
 
     """