Remove unused loop variable.

IPython/core/magics/execution.py

@@ -982,7 +982,7 b' python-profiler package from non-free.""")'
         if number == 0:
             # determine number so that 0.2 <= total time < 2.0
             number = 1
-            for i in range(1, 10):
+            for _ in range(1, 10):
                 if timer.timeit(number) >= 0.2:
                     break
                 number *= 10