media: doc: pixfmt-rgb: Remove layout table for packed RGB formats

The packed RGB formats documentation includes a layout table without any
context. This doesn't bring much useful information, and is confusing at
best. Remove it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>