Regenerate chat client

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/synth.py.
synthtool > Cloning https://github.com/googleapis/discovery-artifact-manager.git.
synthtool > Cleaning output directory.
synthtool > Installing dependencies.
synthtool > Generating chat v1.
synthtool > 	1.28.0
WARNING:root:object without properties Empty: OrderedDict([(u'description', u'A generic empty message that you can re-use to avoid defining duplicated\nempty messages in your APIs. A typical example is to use it as the request\nor the response type of an API method. For instance:\n\n    service Foo {\n      rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);\n    }\n\nThe JSON representation for `Empty` is empty JSON object `{}`.'), (u'type', u'object'), (u'properties', OrderedDict()), (u'id', u'Empty')])
synthtool > 	1.29.2
WARNING:root:object without properties Empty: OrderedDict([(u'description', u'A generic empty message that you can re-use to avoid defining duplicated\nempty messages in your APIs. A typical example is to use it as the request\nor the response type of an API method. For instance:\n\n    service Foo {\n      rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);\n    }\n\nThe JSON representation for `Empty` is empty JSON object `{}`.'), (u'type', u'object'), (u'properties', OrderedDict()), (u'id', u'Empty')])
synthtool > 	1.30.1
WARNING:root:object without properties Empty: OrderedDict([(u'description', u'A generic empty message that you can re-use to avoid defining duplicated\nempty messages in your APIs. A typical example is to use it as the request\nor the response type of an API method. For instance:\n\n    service Foo {\n      rpc Bar(google.protobuf.Empty) returns (google.protobuf.Empty);\n    }\n\nThe JSON representation for `Empty` is empty JSON object `{}`.'), (u'type', u'object'), (u'properties', OrderedDict()), (u'id', u'Empty')])
Writing json metadata to clients/google-api-services-chat/v1.metadata.json
synthtool > Wrote metadata to clients/google-api-services-chat/synth.metadata.