test_optimiser: Remove unused global axis

Failing flake8 test due to unused global variable.

Author: bendudson

freegs/test_optimiser.py

@@ -48,8 +48,8 @@ def test_quadratic():
 
     # Answer should be close to (1,2)
     expected_point = np.array((1, 2))
-    start_distance = np.sqrt(np.sum((expected_point - start_values)**2))
-    result_distance = np.sqrt(np.sum((expected_point - result)**2))
+    start_distance = np.sqrt(np.sum((expected_point - start_values) ** 2))
+    result_distance = np.sqrt(np.sum((expected_point - result) ** 2))
     # It should always get _closer_, even if it doesn't get particularly close
     assert result_distance < start_distance
     assert np.isclose(result_distance, 0, atol=1e-1)
@@ -130,7 +130,6 @@ def test_pick_excludes():
     def monitor(generation, best, pop):
         global best_point
         global pop_points
-        global axis
 
         # Change the color of the previous points
         # to grey and light red