remove unused Maven properties and update Guava to 28.0-android (#1351)
remove unused Maven properties and update Guava to 28.0-android (#1351)

* remove unused variable

* remove unused variable and update guava

* update gson

googleapis/google-api-java-client,googleapis/google-api-java-client,googleapis/google-api-java-client,googleapis/google-api-java-client