media: tegra-vde: remove unused struct 'tegra_vde_h264_frame'

'tegra_vde_h264_frame' has been unused since
commit 313db7d2 ("media: staging: tegra-vde: Remove legacy UAPI
support").

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>