Remove unused usb functions after changing usb mode

Remove unused usb functions after changing usb mode

After setting the new usb mode, the configfs functions that was not used remain.
For example, changing from rndis mode to sdb mode, /sys/kernel/config/usb_gadget/hal-gadget/rndis.default remains.

A functionfs has to do a few extra things.
 - The socket and service associated with functionfs must be terminated.
 - Umount /dev/usb-funcs/[sdb|mtp]/default
 - Delete /dev/usb-funcs/[sdb|mtp]/default recursively

Change-Id: I2d66f033babd5bea20cfc74d8bf23eb9a89c3be1