[usb] Remove unnecessary complete_cb and cookie initializations

With usb request having private regions for each layer in the stack,
the complete callback and their contexts should not be part of the public
part of the usb-request. In previous changes, I have made the complete_cb
and the cookie as parameters. This changeset removes the unnecessary
initializations of these fields. Once all the usage has been removed, I
will remove these fields from the struct.

Test:
Astro: netboot. lsusb.
Pixelbook: fx serve. fx shell. lsusb. bt cli. list adapters.discoverable

Change-Id: I515a9500be75a8b7bd9b67cba4c64534d5372913
5 files changed