Removed unnecessary global variables

Removed three variables set to global, which were all used only in their
respective "main" function.

qubesmanager/bootfromdevice.py

@@ -114,8 +114,6 @@ class VMBootFromDeviceWindow(ui_bootfromdevice.Ui_BootDialog, QtGui.QDialog):
 parser = firewall.qubesadmin.tools.QubesArgumentParser(vmname_nargs=1)
 
 def main(args=None):
-    global bootfromdevice_window
-
     args = parser.parse_args(args)
     vm = args.domains.pop()
 

qubesmanager/global_settings.py

@@ -314,8 +314,6 @@ def handle_exception(exc_type, exc_value, exc_traceback):
 
 
 def main():
-
-    global qtapp
     qtapp = QtGui.QApplication(sys.argv)
     qtapp.setOrganizationName("The Qubes Project")
     qtapp.setOrganizationDomain("http://qubes-os.org")
@@ -325,7 +323,6 @@ def main():
 
     app = Qubes()
 
-    global global_window
     global_window = GlobalSettingsWindow(qtapp, app)
 
     global_window.show()

qubesmanager/settings.py

@@ -954,8 +954,6 @@ parser.set_defaults(
 )
 
 def main(args=None):
-    global settings_window
-
     args = parser.parse_args(args)
     vm = args.domains.pop()