KVM: x86: remove stale comment from struct x86_emulate_ctxt

Commit c44b4c6a ("KVM: emulate: clean up initializations in
init_decode_cache") did some field shuffling and instead of
[opcode_len, _regs) started clearing [has_seg_override, modrm).
The comment about clearing fields altogether is not true anymore.

Fixes: c44b4c6a

 ("KVM: emulate: clean up initializations in init_decode_cache")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>