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>`
Fixes: #8359
Trying to reactivate a user with the admin API (`PUT /_synapse/admin/v2/users/<user_name>`) causes an internal server error.
Seems to be a regression in #8033.