Delete observation API endpoint

[adriantpaez]

Original issue: fibercrypto/skyxcommons#10 (comment)

[DELETE] /api/balances/{address}/observation

Should forget the wallet address and stop observing its balance.

Errors:
■ 204 No content - specified address is not observed

Python implementation

@api.route('/balances/<string:address>/observation', methods=['DELETE'])
def delete_observation(address):
    """
    Delete the specified address from observation list
    """

    result = delete_address_observation(address)

    # if successfully deleted from observation list, return a plain 200
    if "error" in result:
        return make_response(jsonify(build_error(result["error"])), result["status"])
    else:
        return ""