[OpenSCAD] Minor fixes from LGTM analysis

src/Mod/OpenSCAD/exportCSG.py

@@ -29,18 +29,15 @@ __title__="FreeCAD OpenSCAD Workbench - CSG exporter Version"
 __author__ = "Keith Sloan <keith@sloan-home.co.uk>"
 __url__ = ["http://www.sloan-home.co.uk/Export/Export.html"]
 
-import FreeCAD, os, Part, math
-from FreeCAD import Vector
+import FreeCAD
 
 if FreeCAD.GuiUp:
-    import FreeCADGui
     gui = True
 else:
     gui = False
 
 #***************************************************************************
 # Tailor following to your requirements ( Should all be strings )          *
-global fafs
 #fafs = '$fa = 12, $fs = 2'
 #convexity = 'convexity = 10'
 params = FreeCAD.ParamGet("User parameter:BaseApp/Preferences/Mod/OpenSCAD")