Remove logic for psutil < 2.0

... because the minimum version is now 3.2.2.

Also the children method returns a list so we don't have to cast it
to a list explicitly.

Change-Id: I59c1a7847c5b4cc8471884671e57f3e49e4573d8

os_refresh_config/os_refresh_config.py

@@ -60,13 +60,7 @@ PHASES = ['pre-configure',
 
 def timeout():
     p = psutil.Process()
-    try:
-        # psutils version >= 2
-        children = list(p.children(recursive=True))
-    except AttributeError:
-        children = list(p.get_children(recursive=True))
-
-    for child in children:
+    for child in p.children(recursive=True):
         child.kill()