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

Revert r559792 to unbreak INDEX and bulk -a
It seems a lot of reverse dependencies were missed

With hat:	portmgr

Remove most expired ports that depend on Python 2.7:

Exceptions are:
- mail/mailman, our listservers still use it
- www/chromium, solely because of popular demand,
  upstream is (slowly) working on porting it to Python 3
- ports that have actual patches for Python 3 against
  them (Cinnamon and a few unrelated other ports)
- llvm70 and qt5-webengine because they seem to have a lot
  of dependencies which need further analysis
- sysutils/uefi-edk2-bhyve because bhyve seems to use them
- python2 and python27 themselves

I'm sure there will be complaints, but the nice thing about
a version control system is that we can revert and adjust things.

- Add new port devel/electron5
- This is in preparation for the upcoming editors/atom update
- devel/electron4 will be kept because I'm planning to port an app depending on
it

Approved by:	ehaupt (mentor)