Revert "ANDROID: KVM: arm64: Add initial support for KVM_CAP_EXIT_HYPERCALL"

This reverts commit a1bd2a6b.

This capability is unused, so remove it to avoid UAPI divergence from
upstream.

Bug: 226564150
[willdeacon@: Also removed additional instance in arch/arm64/kvm/arm.c]
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: Ib3e929a5fc81dc5c9c1ff8512d48f63bdda5c404