Revert "ANDROID: KVM: arm64: Allow userspace to receive SHARE and UNSHARE notifications"

This reverts commit 0b7e337b.

These notifications are unused by crosvm and are no longer required now
that the host takes care of injecting a SEGV on an illegal memory access
from userspace.

Bug: 226564150
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I22c3e49b4aa5f023961c8849b79e2e0a21ebf0c1