V4L/DVB (5083): Pvrusb2: Remove automodeswitch control

The automodeswitch control was a feature that enable automatic radio /
tv switching based on the selected frequency.  However since frequency
ranges can overlap and also since apparently in some cases it's
possible for the same frequency range to be both tv and radio in a
specific region, then this feature can't safely work.  So it's removed.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>