KVM: x86: Revert "KVM: x86: Mark GPRs dirty when written"

Revert the dirty/available tracking of GPRs now that KVM copies the GPRs
to the GHCB on any post-VMGEXIT VMRUN, even if a GPR is not dirty.  Per
commit de3cd117 ("KVM: x86: Omit caching logic for always-available
GPRs"), tracking for GPRs noticeably impacts KVM's code footprint.

This reverts commit 1c04d8c9

.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210122235049.3107620-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>