Merge pull request #7519 from matrix-org/rav/kill_py2_code

changelog.d/7519.misc

scripts-dev/convert_server_keys.py

synapse/http/matrixfederationclient.py

synapse/logging/utils.py

synapse/push/httppusher.py

synapse/replication/slave/storage/_base.py

synapse/replication/slave/storage/presence.py

synapse/rest/media/v1/_base.py

synapse/storage/_base.py

synapse/storage/data_stores/main/keys.py

synapse/storage/data_stores/main/roommember.py

synapse/storage/data_stores/main/state.py

synapse/storage/data_stores/main/transactions.py

synapse/storage/database.py

synapse/util/caches/__init__.py

synapse/util/stringutils.py