**Apache Airflow version**: 2.0.0b2

**What happened**:

Starting in 2.0.0b2, extras that aren't also providers like `statsd` prevents Airflow from being installed.

**How to reproduce it**:
```
$ docker run --rm -ti python:3.6 bash
# pip install apache-airflow[statsd]==2.0.0b2
Collecting apache-airflow[statsd]==2.0.0b2                 
  Downloading apache_airflow-2.0.0b2-py3-none-any.whl (4.5 MB)                    
...
Collecting statsd<4.0,>=3.3.0; extra == "statsd"          
  Downloading statsd-3.3.0-py2.py3-none-any.whl (11 kB)
ERROR: Could not find a version that satisfies the requirement apache-airflow-providers-statsd; extra == "statsd" (from apache-airflow[statsd]==2.0.0b2) (from versions: none)         
ERROR: No matching distribution found for apache-airflow-providers-statsd; extra == "statsd" (from apache-airflow[statsd]==2.0.0b2)
```

I believe this is from https://github.com/apache/airflow/pull/12233
setup.py
'pagerduty': pagerduty,
    'papermill': papermill,
    'password': password,
    'pinot': pinot,  
    'plexus': plexus,
    'postgres': postgres,
    'presto': presto,
    'qds': qubole,  
    'qubole': qubole,
    'rabbitmq': rabbitmq,
    'redis': redis,
    'salesforce': salesforce,
    'samba': samba,
    'segment': segment,
    'sendgrid': sendgrid,
    'sentry': sentry,
    'singularity': singularity,
    'slack': slack,
    'snowflake': snowflake,
    'spark': spark,
    'ssh': ssh,
    'statsd': statsd,
    'tableau': tableau,
    'vertica': vertica,
    'virtualenv': virtualenv,
    'webhdfs': webhdfs,  
    'winrm': winrm,  
    'yandexcloud': yandexcloud,
}
EXTRAS_PROVIDERS_PACKAGES: Dict[str, Iterable[str]] = {