Remove deprecated Elasticsearch Configs (#12296)
Remove deprecated Elasticsearch Configs (#12296)

Since Airflow 1.10.4 we have removed `elasticsearch_` prefix from all
config items under `[elasticsearch]` section. It is time we remove them
from 2.0.

https://github.com/apache/airflow/blob/1.10.4/UPDATING.md#changes-in-writing-logs-to-elasticsearch


airbnb/airflow,apache/incubator-airflow,DinoCow/airflow,nathanielvarona/airflow,dhuang/incubator-airflow,nathanielvarona/airflow,mrkm4ntr/incubator-airflow,dhuang/incubator-airflow,bolkedebruin/airflow,mistercrunch/airflow,bolkedebruin/airflow,lyft/incubator-airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,Acehaidrey/incubator-airflow,apache/airflow,apache/airflow,dhuang/incubator-airflow,cfei18/incubator-airflow,DinoCow/airflow,mistercrunch/airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,mrkm4ntr/incubator-airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,danielvdende/incubator-airflow,sekikn/incubator-airflow,Acehaidrey/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,DinoCow/airflow,danielvdende/incubator-airflow,apache/airflow,apache/airflow,mrkm4ntr/incubator-airflow,mrkm4ntr/incubator-airflow,cfei18/incubator-airflow,apache/incubator-airflow,sekikn/incubator-airflow,nathanielvarona/airflow,apache/airflow,bolkedebruin/airflow,apache/incubator-airflow,nathanielvarona/airflow,dhuang/incubator-airflow,cfei18/incubator-airflow,sekikn/incubator-airflow,airbnb/airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,mistercrunch/airflow,apache/incubator-airflow,airbnb/airflow,cfei18/incubator-airflow,danielvdende/incubator-airflow,bolkedebruin/airflow,airbnb/airflow,mistercrunch/airflow,apache/airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,DinoCow/airflow