* [youtube] Fix `--youtube-skip-dash-manifest`
* [build] Use `$()` in `Makefile`. Closes#3684
* Fix bug in 385ffb467b
* Fix bug in 43d7f5a5d0
* [cleanup] Remove unnecessary `utf-8` from `str.encode`/`bytes.decode`
* [utils] LazyList: Expose unnecessarily "protected" attributes
and other minor cleanup
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
From now on, the line
from __future__ import unicode_literals
should be contained in every single Python file lest we run into any more 2.x/3.x issues.
Going forward, we're likely to develop on 3.x only and would likely miss subtle bugs otherwise.
