[mojo-edk] Remove invalid DCHECK from early Mach port message processing

This DCHECK is clearly not intentional and can't possibly be correct.
It's not being hit in practice today due to the latency of ChannelMojo
setup, but reducing that latency easily exposes it.

TBRing because it's trivial.

BUG=None
TBR=yzshen@chromium.org

Review-Url: https://codereview.chromium.org/2178633002
Cr-Commit-Position: refs/heads/master@{#407261}

mojo/edk/system/node_channel.cc

@@ -771,7 +771,6 @@ void NodeChannel::ProcessPendingMessagesWithMachPorts() {
     pending_writes.swap(pending_write_messages_);
     pending_relays.swap(pending_relay_messages_);
   }
-  DCHECK(pending_writes.empty() && pending_relays.empty());
 
   while (!pending_writes.empty()) {
     Channel::MessagePtr message = std::move(pending_writes.front());