Remove deprecated features prior to releasing Airflow 2.0

[dimberman]

Ticket was created 02/May/16 13:00

Description

A number of features have been marked for deprecation in Airflow 2.0. They need to be deleted prior to release.

Usually the error message or comments will mention Airflow 2.0 with either a #TODO or #FIXME.

Tracking list (not necessarily complete!):
JIRA:
AIRFLOW-31
AIRFLOW-200

GitHub:
https://github.com/airbnb/airflow/pull/1137/files#diff-1c2404a3a60f829127232842250ff406R233
#1219
#1285

Use case / motivation

Related Issues

Moved here from https://issues.apache.org/jira/browse/AIRFLOW-32

[vikramkoka]

@dimberman Is there anything left to do here?