Remove _PY3 checks in a bunch of places

[twisted-trac]

	@rodrigc reported
Trac ID	trac#9842
Type	enhancement
Created	2020-05-31 17:29:43Z

Now that Twisted only supports Python 3.5 and higher,
we can remove checks for _PY3 in a bunch of places.

This eliminates a bunch of errors reported by mypy when doing:

tox -e mypy

Searchable metadata

trac-id__9842 9842
type__enhancement enhancement
reporter__rodrigc rodrigc
priority__normal normal
milestone__publish_types publish types
branch__ 
branch_author__ 
status__closed closed
resolution__fixed fixed
component__core core
keywords__None None
time__1590946183124156 1590946183124156
changetime__1594360403322407 1594360403322407
version__None None
owner__Craig_Rodrigues__rodrigc_____ Craig Rodrigues <rodrigc@...>

[twisted-trac]

	@rodrigc commented

#1285

[twisted-trac]

	@rodrigc commented

Approved here: #1285 (review)

[twisted-trac]

	@rodrigc set owner to @rodrigc @rodrigc set status to closed

In changeset 70522c1

#!CommitTicketReference repository="" revision="70522c1b48b7a6ba29b18a080c12464d865b9e22"
Merge pull request #1285 from twisted/9842-rodrigc-no-py3

Remove some _PY3 checks and eliminate Python2 only code

Author: rodrigc
Reviewer: adiroiban
Fixes: ticket:9842