Revert "usb: gadget: Introduce free_usb_request helper"

This reverts commit 70a76674 which is
commit 201c53c6 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I1faed118a5138d00df06ff7074b4f493cc56f29b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>