**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
'google-cloud-spanner>=1.10.0,<2.0.0',
    'google-cloud-speech>=0.36.3,<2.0.0',
    'google-cloud-storage>=1.16,<2.0.0',
    'google-cloud-tasks>=1.2.1,<2.0.0',
    'google-cloud-texttospeech>=0.4.0,<2.0.0',
    'google-cloud-translate>=1.5.0,<2.0.0',
    'google-cloud-videointelligence>=1.7.0,<2.0.0',
    'google-cloud-vision>=0.35.2,<2.0.0',
    'grpcio-gcp>=0.2.2',
    'pandas-gbq',
]
grpc = [
    'google-auth>=1.0.0, <2.0.0dev',
    'google-auth-httplib2>=0.0.1',
    'grpcio>=1.15.0',
]
hashicorp = [
    'hvac~=0.10',
]
hdfs = [
    'snakebite-py3',
]
hive = [
    'hmsclient>=0.1.0',
    'pyhive[hive]>=0.6.0',
]
jdbc = [
    'jaydebeapi>=1.1.1',
]
jenkins = [