Use parse_json_object_from_request to parse JSON out of request bodies

synapse/federation/transport/server.py

synapse/http/servlet.py

synapse/rest/client/v1/presence.py

synapse/rest/client/v1/profile.py

synapse/rest/client/v1/room.py

synapse/rest/client/v2_alpha/account_data.py

synapse/rest/client/v2_alpha/filter.py

synapse/rest/client/v2_alpha/keys.py

synapse/rest/client/v2_alpha/tags.py

synapse/rest/key/v2/remote_key_resource.py

tests/rest/client/v1/test_profile.py