cc/blimp: Proto Cleanup.

cc/proto/compositor_message.proto

Index: cc/proto/compositor_message.proto
diff --git a/cc/proto/compositor_message.proto b/cc/proto/compositor_message.proto
index 94cf6bf98232fd1ecd6ab7ff0d9d527d7b61f170..93dc438a38af1b870cfeaeecb17a4a6677484786 100644
--- a/cc/proto/compositor_message.proto
+++ b/cc/proto/compositor_message.proto
@@ -7,8 +7,6 @@ syntax = "proto2";
 option optimize_for = LITE_RUNTIME;
 
 import "client_state_update.proto";
-import "compositor_message_to_impl.proto";
-import "compositor_message_to_main.proto";
 import "layer_tree_host.proto";
 
 package cc.proto;
@@ -39,8 +37,4 @@ message CompositorMessage {
   // state on the engine, the ack will always be bundled with the resulting
   // frame update.
   optional bool client_state_update_ack = 6;
-
-  // One of these is set based on where the message is going to.
-  optional CompositorMessageToMain to_main = 1;
-  optional CompositorMessageToImpl to_impl = 2;
 }