Remove proxies argument for async client

[jjkoh95]

Description

• remove arg proxies

Related Issue

• AsyncClient.post() got an unexpected keyword argument 'proxies' #190

Motivation and Context

• remove arg proxies in async client (should have been already handled during init)
• https://www.python-httpx.org/advanced/

How Has This Been Tested?

Tested by pip installing branch, and then run sample code (check screenshots below)

pip install git+ssh://git@github.com/jjkoh95/Bard-API.git@remove-proxies-arg

Screenshots (if appropriate):

[dsdanielpark]

Thank you for your contribution! Have a nice day.