Staging: rtxxx0: remove dead platform specific code

Remove dead support for:

* IKANOS_VX_1X0
* INF_TWINPASS
* INF_DANUBE
* BRCM_6358

platforms.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>