This reverts commit 05e8c70c.

This basically speeds up federation by "squeezing" each individual dual database call (to destinations and destination_rooms), which previously happened per every event, into one call for an entire batch (100 max).

Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>

Part of #9744

Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.

`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl&gt;`>

 - Update black version to the latest
 - Run black auto formatting over the codebase
    - Run autoformatting according to [`docs/code_style.md
`](https://github.com/matrix-org/synapse/blob/80d6dc9783aa80886a133756028984dbf8920168/docs/code_style.md)
 - Update `code_style.md` docs around installing black to use the correct version

Run `isort`, `flake8` and `black` over the `contrib/` directory and `synctl` script. The latter was already being done in CI, but now the linting script does it too.

Fixes https://github.com/matrix-org/synapse/issues/7910

* Fix deprecation warnings due to invalid escape sequences.

* Add changelog

Signed-off-by: Karthikeyan Singaravelan <tir.karthi@gmail.com>

* update version of black and also fix the mypy config being overridden

fix the copyright holder from matrix.org to OpenMarket Ltd, as matrix.org hasn't been incorporated in time for launch.

add in copyrights to everything, not just the synapse subdir, and add a copyrighter.pl whilst we're at it