Use ChannelMojo for remote security key channels.

remoting/host/security_key/BUILD.gn

Index: remoting/host/security_key/BUILD.gn
diff --git a/remoting/host/security_key/BUILD.gn b/remoting/host/security_key/BUILD.gn
index 8008b74d2fbb6a4b821fc324e85d193a807f5a4a..b67c51798942b4ce3fedf3eec32348c8c2712a14 100644
--- a/remoting/host/security_key/BUILD.gn
+++ b/remoting/host/security_key/BUILD.gn
@@ -36,6 +36,7 @@ source_set("security_key") {
   ]
 
   deps = [
+    "//mojo/edk/system",
     "//remoting/proto",
     "//third_party/webrtc/modules/desktop_capture",
   ]
@@ -90,14 +91,15 @@ source_set("unit_tests") {
   public_deps = [
     ":test_support",
   ]
+  deps = [
+    "//mojo/edk/test:test_support",
+  ]
 }
 
 static_library("test_support") {
   testonly = true
 
   sources = [
-    "fake_ipc_security_key_auth_handler.cc",
-    "fake_ipc_security_key_auth_handler.h",
     "fake_security_key_ipc_client.cc",
     "fake_security_key_ipc_client.h",
     "fake_security_key_ipc_server.cc",