Remove code relating to guest reporting stackoverflow

[ludfjig]

StackOverflow is currently detected in 3 different ways:

1. Hypervisor detects the guest writing to the stack guard page, which host reports as a stackoverflow
2. Host checks stack guard canary after guest returns and makes sure it's not modified
3. The guest itself somehow identifies a stackoveflow and then aborts with a specific error code, which host reports as a stackoverflow

I believe the third is dead code, as I cannot find anywhere in our code where the guest itself reports this error code. I believe it was previously used when dynamically allocating stack, but not anymore, so we should consider removing this dead code in the host