Multiple modules required by apache-airflow is missing when installed with `python setup.py install`

After installation with `python setup.py install`, performed in the git cloned latest master branch, the command `airflow -h` raises the following error
```python
import httpx
File "/opt/anaconda3/lib/python3.8/site-packages/httpx-0.19.0-py3.8.egg/httpx/__init__.py", line 2, in
from ._api import delete, get, head, options, patch, post, put, request, stream
File "/opt/anaconda3/lib/python3.8/site-packages/httpx-0.19.0-py3.8.egg/httpx/_api.py", line 4, in
from ._client import Client
File "/opt/anaconda3/lib/python3.8/site-packages/httpx-0.19.0-py3.8.egg/httpx/_client.py", line 9, in
from ._auth import Auth, BasicAuth, FunctionAuth
File "/opt/anaconda3/lib/python3.8/site-packages/httpx-0.19.0-py3.8.egg/httpx/_auth.py", line 10, in
from ._models import Request, Response
File "/opt/anaconda3/lib/python3.8/site-packages/httpx-0.19.0-py3.8.egg/httpx/_models.py", line 11, in
import charset_normalizer
ModuleNotFoundError: No module named 'charset_normalizer'
```
And pip installation of the "NotFound" modules leads to various "version incompatible" issues.

Start by reproducing the issue with `python setup.py install` from the latest master, then run `airflow -h` and inspect the package's setup.py dependency declarations. Check why httpx's required `charset_normalizer` dependency is absent or incompatible after installation. Done means a clean install provides compatible dependencies and the command starts without this import error.

Written by the indexing model from the issue text.