media: exynos-gsc: Drop obsolete capabilities

Setting both V4L2_CAP_VIDEO_CAPTURE_MPLANE and V4L2_CAP_VIDEO_OUTPUT_MPLANE
for mem2mem video nodes is obsolete since commit f0476a83 ("[media]
V4L: Add capability flags for memory-to-memory devices"). It was enough
time to adapt all users to the new flags, so drop the legacy caps for now
to match other mem2mem drivers.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>