Move node() == nullptr check into //aos:configuration

This simplifies the code surprisingly significantly for dealing with
single node systems.

Change-Id: Ib317e16a9055fbf1341a194120a5b34f05b2d8f8
diff --git a/aos/events/simulated_event_loop.cc b/aos/events/simulated_event_loop.cc
index 578e151..a2740e4 100644
--- a/aos/events/simulated_event_loop.cc
+++ b/aos/events/simulated_event_loop.cc
@@ -473,13 +473,11 @@
   ChannelIndex(channel);
   Take(channel);
 
-  if (node() != nullptr) {
-    if (!configuration::ChannelIsReadableOnNode(channel, node())) {
-      LOG(FATAL) << "Channel { \"name\": \"" << channel->name()->string_view()
-                 << "\", \"type\": \"" << channel->type()->string_view()
-                 << "\" } is not able to be watched on this node.  Check your "
-                    "configuration.";
-    }
+  if (!configuration::ChannelIsReadableOnNode(channel, node())) {
+    LOG(FATAL) << "Channel { \"name\": \"" << channel->name()->string_view()
+               << "\", \"type\": \"" << channel->type()->string_view()
+               << "\" } is not able to be watched on this node.  Check your "
+                  "configuration.";
   }
 
   std::unique_ptr<SimulatedWatcher> shm_watcher(
@@ -500,13 +498,11 @@
     const Channel *channel) {
   ChannelIndex(channel);
 
-  if (node() != nullptr) {
-    if (!configuration::ChannelIsReadableOnNode(channel, node())) {
-      LOG(FATAL) << "Channel { \"name\": \"" << channel->name()->string_view()
-                 << "\", \"type\": \"" << channel->type()->string_view()
-                 << "\" } is not able to be fetched on this node.  Check your "
-                    "configuration.";
-    }
+  if (!configuration::ChannelIsReadableOnNode(channel, node())) {
+    LOG(FATAL) << "Channel { \"name\": \"" << channel->name()->string_view()
+               << "\", \"type\": \"" << channel->type()->string_view()
+               << "\" } is not able to be fetched on this node.  Check your "
+                  "configuration.";
   }
 
   return GetSimulatedChannel(channel)->MakeRawFetcher(this);