Revert "init: support 2SI devices with skip_initramfs"

[vvb2060]

This reverts commit b38fd1ca5f15ed22858c7737879c38d360e78eac.

[aviraxp]

I think this is ready for merge.

[vvb2060]

We need to detect /dev/root at runtime and then write it to config in boot.img, which is the only effective way to detect legacy SAR.

[topjohnwu]

We'll find another way to detect the scenario, let's revert the behavior back to what it was