media: docs: v4l2-controls: remove outdated paragraph

This paragraph was added by commit a42b57f5 ("V4L/DVB: Documentation:
add v4l2-controls.txt documenting the new controls API") back in 2010, when
the controls API has been improved. Nowadays it is a bit anachronistic, so
remove it.

The same information is stated in up-to-date wording a few paragraphs later

> You’re done! And this is sufficient for most of the drivers we have. No
> need to do any validation of control values, or implement QUERYCTRL,
> QUERY_EXT_CTRL and QUERYMENU. And G/S_CTRL as well as G/TRY/S_EXT_CTRLS
> are automatically supported.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>