client: Remove useless except in ipa-client-install

SystemExit is raised by sys.exit() so catching and reraising it again is
wasting of resources

https://fedorahosted.org/freeipa/ticket/6392

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

client/ipa-client-install

@@ -260,8 +260,6 @@ def main():
 try:
     if __name__ == "__main__":
         sys.exit(main())
-except SystemExit as e:
-    sys.exit(e)
 except KeyboardInterrupt:
     sys.exit(1)
 except RuntimeError as e: