media: docs: cleanup bttv-devel.rst file

This file was converted from text at the early ReST days.
We learnt a lot about how to produce a nicer result while
keeping the file better readable as plain text.

Change some ReST markups to make it look better, both at
the output formats and as plain text file.

While here, remove references for the old bt848/winutil
tool, as it seems that it doesn't exist anymore.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>