refactor(flowable): remove unnecessary inheritance from FlowableBufferTimedFlushable

Add CHANGELOG.md for the refactoring.

Author: OrezzerO

CHANGELOG.md

@@ -24,6 +24,7 @@
       - [Generated REST API Documentation](https://docs.influxdata.com/influxdb/v2/api/v1-compatibility/#operation/PostQueryV1)
       - [Influx 1.1 query compatibility](https://docs.influxdata.com/influxdb/latest/reference/api/influxdb-1x/query/)
    - See the updated InfluxQLExample
+- [#794](https://github.com/influxdata/influxdb-client-java/issues/794): Delete unnecessary inheritance of FlowableBufferTimedFlushable.
 
 ### Bug Fixes