Remove shebang line from module files (#10415)

changelog.d/10415.misc

synapse/_scripts/review_recent_signups.py

synapse/app/admin_cmd.py

synapse/app/appservice.py

synapse/app/client_reader.py

synapse/app/event_creator.py

synapse/app/federation_reader.py

synapse/app/federation_sender.py

synapse/app/frontend_proxy.py

synapse/app/generic_worker.py

synapse/app/homeserver.py

synapse/app/media_repository.py

synapse/app/pusher.py

synapse/app/synchrotron.py

synapse/app/user_dir.py

synapse/push/pusherpool.py

synapse/util/versionstring.py