Some simplifications for package serialization.

PiperOrigin-RevId: 183842057
diff --git a/src/main/java/com/google/devtools/build/lib/packages/Package.java b/src/main/java/com/google/devtools/build/lib/packages/Package.java
index b07d02a..4bbd3bf 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/Package.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/Package.java
@@ -1585,7 +1585,7 @@
     @Override
     public void serialize(
         PackageCodecDependencies codecDeps, Package input, CodedOutputStream codedOut)
-        throws IOException {
+        throws IOException, SerializationException {
       codecDeps.getPackageSerializer().serialize(input, codedOut);
     }