Rewrote square function using iteration.

- No, the wording of the lab was a little confusing because it says to use
list iteration but you don't actually need a list for it. Also, the function
still "calls" forward and right four times; we only wrote it once.

square.py

@@ -1,14 +1,9 @@
 from turtle import *
 
 def square(side_length):
-    forward(side_length)
-    right(90)
-    forward(side_length)
-    right(90)
-    forward(side_length)
-    right(90)
-    forward(side_length)
-    right(90)
+    for _ in range(4):
+        forward(side_length)
+        right(90)
 
 sizes = [20, 40, 60, 80, 100]
 for size in sizes: