With the patch in D29735 you actually can see the real flavor warnings again. Fix those.
Suggested commit message
Fix all cases where 'Moved to' points to a non existing flavor.
PHP 7.1, 7.2 and Python 3.5 were removed from the tree. Mark the ports
as removed and use the original removal date and reason of the 3
aforementioned ports respectively.
One exception devel/py3-flake8-builtins pointed to the py36 flavor but
only supports Python 3.7+ now, just point it to @py37.
Fix one more "normal" warning that was introduced sine the last