[ssh] Stop depending on developer-keys target

This target is being removed in favor of including SSH keys via
'fx'.

Change-Id: Ia955e58a2380eafb7d7d8232d453f64a40215062
diff --git a/garnet/packages/config/BUILD.gn b/garnet/packages/config/BUILD.gn
index 49527c3..4f846b1 100644
--- a/garnet/packages/config/BUILD.gn
+++ b/garnet/packages/config/BUILD.gn
@@ -40,7 +40,7 @@
 group("openssh_keys") {
   testonly = true
   public_deps = [
-    "//third_party/openssh-portable/fuchsia/developer-keys",
+    "//third_party/openssh-portable/fuchsia/developer-keys:ssh_config",
   ]
 }