Remove a few expired ports depending on Python 2.7:

2020-12-31 www/iridium: Uses Python 2.7 which is EOLed upstream
2020-12-31 editors/atom: Uses Python 2.7 which is EOLed upstream
2020-12-31 devel/electron4: Uses Python 2.7 which is EOLed upstream
2020-12-31 devel/electron5: Uses Python 2.7 which is EOLed upstream
2020-12-31 devel/electron6: Uses Python 2.7 which is EOLed upstream