media: venus: core: Drop second v4l2 device unregister

Wrong solution of rebase conflict leads to calling twice
v4l2_device_unregister in .venus_remove. Delete the second one.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>