media: uapi: vp8: Remove "header" from symbol names and macros

It doesn't seem to add any clarity to have a "header" suffix in controls,
struct names and flags.

Since this just makes names too long without any benefit, just drop it.

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>