V4L/DVB (4887): Remove the broken VIDEO_ZR36120 driver

The VIDEO_ZR36120 driver has:
- already been marked as BROKEN in 2.6.0 three years ago and
- is still marked as BROKEN.
Drivers that had been marked as BROKEN for such a long time seem to be 
unlikely to be revived in the forseeable future.
But if anyone wants to ever revive this driver, the code is still 
present in the older kernel releases.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Acked-by: Mauro Carvalho Chehab <mchehab@infradead.org>