Remove syutil dependency in favour of smaller single-purpose libraries

synapse/config/key.py

synapse/crypto/event_signing.py

synapse/crypto/keyring.py

synapse/http/client.py

synapse/http/matrixfederationclient.py

synapse/http/server.py

synapse/python_dependencies.py

synapse/rest/client/v1/voip.py

synapse/rest/client/v2_alpha/keys.py

synapse/rest/key/v1/server_key_resource.py

synapse/rest/key/v2/local_key_resource.py

synapse/storage/event_federation.py

synapse/storage/events.py

synapse/storage/keys.py

synapse/storage/pusher.py

synapse/storage/signatures.py

synapse/storage/transactions.py