remove unnecessary type conversion

This removes the ```float()``` around a (potential) integer division.
Since Python3 the result of an integer division is a floating
point number. This also removes the time and attention capacity
necessary by learners for an explaination of what this does and
why it is there. I do not mean to say that type conversions cannot
be important, but the focus of this excercise is elsewhere.

Note: it was good to have this in place for Python2, but Python2
is dead today and has been for a while. We also require an installation
of Python3 in the setup.

Author: knarrff

_episodes/10-defensive.md

@@ -130,10 +130,10 @@ def normalize_rectangle(rect):
     dx = x1 - x0
     dy = y1 - y0
     if dx > dy:
-        scaled = float(dx) / dy
+        scaled = dx / dy
         upper_x, upper_y = 1.0, scaled
     else:
-        scaled = float(dx) / dy
+        scaled = dx / dy
         upper_x, upper_y = scaled, 1.0
 
     assert 0 < upper_x <= 1.0, 'Calculated upper X coordinate invalid'