*: remove unused imports

tests/compat/test_fsm.py

@@ -1,5 +1,4 @@
 import unittest
-from itertools import count
 
 from nmigen.compat import *
 from nmigen.compat.genlib.fsm import FSM

tests/test_sim.py

@@ -1,7 +1,7 @@
 import os
 from contextlib import contextmanager
 
-from nmigen._utils import flatten, union
+from nmigen._utils import flatten
 from nmigen.hdl.ast import *
 from nmigen.hdl.cd import  *
 from nmigen.hdl.mem import *

tests/utils.py

@@ -5,7 +5,6 @@ import subprocess
 import textwrap
 import traceback
 import unittest
-from contextlib import contextmanager
 
 from nmigen.hdl.ast import *
 from nmigen.hdl.ir import *