media: videodev2.h: Remove unneeded comment about 4CC value

The V4L2_PIX_FMT_BGRA444 format has a comment that explains why its 4CC
value is GA12. This explains the development history and isn't of much
interest to readers, it should have been part of a commit message
instead. Drop the comment, anyone interested in history can turn to git.

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>