accel/mshv: Remove remap overlapping mappings code

accel/mshv: Remove remap overlapping mappings code

This change removes userland code that worked around a restriction
in the mshv driver in the 6.18 kernel: regions from userland
couldn't be mapped to multiple regions in the kernel. We maintained a
shadow mapping table in qemu and used a heuristic to swap in a requested
region in case of UNMAPPED_GPA exits.

However, this heuristic wasn't reliable in all cases, since HyperV
behaviour is not 100% reliable across versions. HyperV itself doesn't
prohibit to map regions at multiple places into the guest, so the
restriction has been removed in the mshv driver.

Hence we can remove the remapping code. Effectively this will mandate a
6.19 kernel, if the workload attempt to map e.g. BIOS to multiple
reagions. I still think it's the right call to remove this logic:

- The workaround only seems to work reliably with a certain revision
  of HyperV as a nested hypervisor.
- We expect Direct Virtualization (L1VH) to be the main platform for
  the mshv accelerator, which also requires a 6.19 kernel

This reverts commit efc4093358511a58846a409b965213aa1bb9f31a.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Acked-by: Wei Liu (Microsoft) <wei.liu@kernel.org>
Tested-by: Mohamed Mediouni <mohamed@unpredictable.fr>
Link: https://lore.kernel.org/r/20260113153708.448968-1-magnuskulke@linux.microsoft.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>