fix(connector):  Refactor capture and refund flow for Connectors (#1821)
Files to modify:


**bitpay.rs**
  Remove:
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body

**coinbase.rs**
  Remove:
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body
    - function: private::build_request
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body

**iatapay.rs**
  Remove:
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body
    - function: private::handle_response

**opennode.rs**
  Remove:
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body
    - function: private::build_request
    - function: private::get_headers
    - function: private::get_content_type
    - function: private::get_url
    - function: private::get_request_body