fix global variables for flake8

Author: jgressier

aerokit/common/defaultgas.py

@@ -26,6 +26,6 @@ def save_default():
     _saved_gamma = _gamma
 
 def restore_default():
-    global _saved_r, _saved_gamma, _r, _gamma
+    global _r, _gamma
     _r = _saved_r
     _gamma = _saved_gamma