[AIRFLOW-XXX] Remove default/wrong values from test config. (#5684)
[AIRFLOW-XXX] Remove default/wrong values from test config. (#5684)

Most of the values I've removed here are the current defaults, so we
don't need to specify them again.

The reason I am removing them is that `email_backend` of
`airflow.utils.send_email_smtp` has been incorrect since 1.7.2(!) but
hasn't mattered until #5379 somehow triggered it. By removing the
default values it should make it easier to update in future.
danielvdende/incubator-airflow,wileeam/airflow,bolkedebruin/airflow,spektom/incubator-airflow,lyft/incubator-airflow,nathanielvarona/airflow,wooga/airflow,airbnb/airflow,Acehaidrey/incubator-airflow,airbnb/airflow,mtagle/airflow,dhuang/incubator-airflow,DinoCow/airflow,DinoCow/airflow,sekikn/incubator-airflow,bolkedebruin/airflow,lyft/incubator-airflow,sekikn/incubator-airflow,lyft/incubator-airflow,dhuang/incubator-airflow,nathanielvarona/airflow,sekikn/incubator-airflow,bolkedebruin/airflow,danielvdende/incubator-airflow,apache/airflow,cfei18/incubator-airflow,spektom/incubator-airflow,Acehaidrey/incubator-airflow,mtagle/airflow,DinoCow/airflow,apache/incubator-airflow,wooga/airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,apache/incubator-airflow,danielvdende/incubator-airflow,mistercrunch/airflow,apache/airflow,lyft/incubator-airflow,apache/airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,mrkm4ntr/incubator-airflow,DinoCow/airflow,bolkedebruin/airflow,Acehaidrey/incubator-airflow,Fokko/incubator-airflow,apache/airflow,wooga/airflow,mistercrunch/airflow,airbnb/airflow,apache/airflow,mtagle/airflow,mrkm4ntr/incubator-airflow,mistercrunch/airflow,nathanielvarona/airflow,dhuang/incubator-airflow,apache/airflow,Fokko/incubator-airflow,Acehaidrey/incubator-airflow,mtagle/airflow,bolkedebruin/airflow,airbnb/airflow,danielvdende/incubator-airflow,apache/incubator-airflow,mrkm4ntr/incubator-airflow,dhuang/incubator-airflow,danielvdende/incubator-airflow,cfei18/incubator-airflow,nathanielvarona/airflow,Acehaidrey/incubator-airflow,cfei18/incubator-airflow,spektom/incubator-airflow,Fokko/incubator-airflow,sekikn/incubator-airflow,cfei18/incubator-airflow,Fokko/incubator-airflow,cfei18/incubator-airflow,spektom/incubator-airflow,wooga/airflow,mistercrunch/airflow,nathanielvarona/airflow,wileeam/airflow,wileeam/airflow,wileeam/airflow