**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
'jdbc': ["jdbc"],
    'jira': ["jira"],
    'kerberos': [],
    'kubernetes': ["cncf.kubernetes"],  
    'ldap': [],
    "microsoft.azure": ["microsoft.azure"],
    "microsoft.mssql": ["microsoft.mssql"],
    "microsoft.winrm": ["microsoft.winrm"],
    'mongo': ["mongo"],
    'mssql': ["microsoft.mssql"],  
    'mysql': ["microsoft.mssql"],
    'odbc': ["odbc"],
    'oracle': ["oracle"],
    'pagerduty': ["pagerduty"],
    'papermill': ["papermill"],
    'password': [],
    'pinot': ["apache.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"],