[cleanup] Upgrade syntax

Using https://github.com/asottile/pyupgrade

1. `__future__` imports and `coding: utf-8` were removed
2. Files were rewritten with `pyupgrade --py36-plus --keep-percent-format`
3. f-strings were cherry-picked from `pyupgrade --py36-plus`

Extractors are left untouched (except removing header) to avoid unnecessary merge conflicts

1 files changed, 0 insertions, 3 deletions

diff --git a/test/test_postprocessors.py b/test/test_postprocessors.py
index bbe998993..e5893f7d2 100644
--- a/test/test_postprocessors.py
+++ b/test/test_postprocessors.py
@@ -1,7 +1,4 @@
 #!/usr/bin/env python3
-
-from __future__ import unicode_literals
-
 # Allow direct execution
 import os
 import sys