**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
'slack': ["slack"],
    'snowflake': ["snowflake"],
    'spark': ["spark"],
    'ssh': ["ssh"],
    'statsd': ["statsd"],
    'tableau': ["tableau"],
    'vertica': ["vertica"],
    'virtualenv': ["virtualenv"],
    'webhdfs': ["apache.hdfs"],  
    'winrm': ["microsoft.winrm"],  
    'yandexcloud': ["yandexcloud"],
}
devel_all = list(
    set(
        devel
        + [req for req_list in EXTRAS_REQUIREMENTS.values() for req in req_list]
        + [req for req_list in PROVIDERS_REQUIREMENTS.values() for req in req_list]
    )
)
PACKAGES_EXCLUDED_FOR_ALL = []
if PY3:
    PACKAGES_EXCLUDED_FOR_ALL.extend(
        [
            'snakebite',
        ]
    )
PACKAGES_EXCLUDED_FOR_CI = [
    'apache-beam',
]
def is_package_excluded(package: str, exclusion_list: List[str]):