qcom: remove split SC7280 venus firmware images

Qualcomm drivers have supported non-split firmware since since 2019 in
linux kernel commit 498b98e93900 ("soc: qcom: mdt_loader: Support
loading non-split images"). There are no released devices using the
SC7280 chipset, so there is no need to support legacy split images.

I verified that the non-split image is loadable and that the venus
media capabilities are intact without the split images with a ChromeOS
5.15 kernel.

Signed-off-by: Nathan Hebert <nhebert@chromium.org>