[$] Postponing some feature removals in Python 3.9

Python 2 was officially "retired" on the last day of 2019, so no bugswill be fixed or changes made in that version of the language, at least by the coredevelopers-distributions and others will continue for some time tocome. But there are lots of Python projects that still supportPython 2.7 and may not be ready for an immediate clean break. Some changes thatwere made for the upcoming Python 3.9 release (which is currently scheduledfor October) are causing headaches because support for long-deprecated2.7-compatibility features is being dropped. That led to a discussion onthe python-dev mailing list about postponing thosechanges to give a bit more time to projects that want to dropPython 2.7 support soon, but not immediately.