Use only one http client

[dnarcese]

Vision statement / What / Requirements

Currently we are using both HttpUrlConnectionClient and OkHttpClient in different places in the code.

Impact

More consistency if we only use one. Also, there may be certain benefits of one over the other. This could slightly improve performance for users

Acceptance criteria

• One library is decided on
• All usages of the other library are replaced

[mcomella]

I have a WIP in https://github.com/mcomella/firefox-tv/tree/wip-2653-one-http-client