Style(cmp): Fix flake8 warnings F824

The warnings were "`global <...>` is unused: name is never assigned in scope."
Eithe remove `global` or assign a dummy value.

Author: phdru

Cheetah/ImportHooks.py

@@ -37,7 +37,6 @@
 
 
 def setCacheDir(cacheDir):
-    global _cacheDir
     _cacheDir.append(cacheDir)
 
 ##################################################
@@ -144,5 +143,6 @@ def uninstall():
                 del ImportManager._globalOwnerTypes[0]
             del ImportManager.__oldimport__
             global _manager
+            _manager = None
             del _manager
             _installed = False

Cheetah/Tests/Performance.py

@@ -61,7 +61,6 @@ def wrapper(*args, **kw):
                 else:
                     pystone_rate = current_pystone[0] / current_pystone[1]
                     pystone_total_time = total_time / pystone_rate
-                global DEBUG
                 if DEBUG:
                     print('The test "%s" took: %s pystones' % (
                         function.__name__, pystone_total_time))