[DEPR]: Remove EdxRestApiClient from edx-rest-api-client library

[dianakhuang]

As part of the work to complete #189

We would like to:

• Move EdxRestApiClient into a location near where it is used in edx-platform and rename it to DeprecatedRestApiClient
• Remove EdxRestApiClient from https://github.com/openedx/edx-rest-api-client with proper release notes and versioning indicating that it is a breaking release.

[Yagnesh1998]

assign me

[robrap]

@dianakhuang:

1. I don't think @Yagnesh1998 is working on this any longer, so we should probably unassign.
2. It is possible that feat: DEPR EdxRestApiClient edx-rest-api-client#303 is the only remaining work, and was really clost to landing, so we could possibly do this in a DEPR meeting.