Fix up logcontexts

synapse/storage/presence.py

synapse/storage/stream.py

synapse/util/__init__.py

synapse/util/async.py

synapse/util/caches/descriptors.py

synapse/util/caches/snapshot_cache.py

synapse/util/distributor.py

synapse/util/logcontext.py

synapse/util/logutils.py

synapse/util/metrics.py

synapse/util/ratelimitutils.py