Creating actually two issue here for two different WS, if it is preferred to open two issues just let me know.

As per comment of Damyon Wiese to MDL-29472, "Context is considered internal to Moodle - and not exposed to webservices. It should not be sent as a parameter or returned in a response"

FILE: file/externallib.php

FUNCTION: get_files_parameters()
PARAMETER: 'contextid' => new external_value(PARAM_INT, 'context id')

FUNCTION: get_files_returns()
PARAMETER: 'contextid' => new external_value(PARAM_INT, '')

FUNCTION: upload_parameters()
PARAMETER: 'contextid' => new external_value(PARAM_INT, 'context id')

FUNCTION: upload_returns()
PARAMETER: 'contextid' => new external_value(PARAM_INT, '')