uhid_snes: Remove USB_ST_TRANSFERRED handling for the status request.

The result of the request computed in new_status was never returned to
the caller leaving new_status as a set-but-unused variable. Removing
new_status leaves sc->previous_status as a write-only variable.
Removing sc->previous_status leaves current_status as a write-only
variable, so it collapses down to removing the entire
USB_ST_TRANSFERRED case.

Arguably, all of the support for UHID_SNES_STATUS_DT_RD should be
removed as it doesn't return anything to the caller. If the request
should be fixed instead then this commit should be reverted and
new_status should be returned to whoever submitted the request.

Differential Revision: https://reviews.freebsd.org/D34840