Java: Address review comments.

Author: michaelnebel

java/ql/lib/semmle/code/java/dataflow/internal/ExternalFlowExtensions.qll

@@ -34,7 +34,10 @@ extensible predicate neutralModel(
 );
 
 /**
- * DEPRECATED: Do not use.
+ * INTERNAL: Do not use.
+ *
+ * DEPRECATED: This predicate is only intended for adding models used by experimental queries.
+ * This predicate will be deleted in the future.
  *
  * Holds if an experimental source model exists for the given parameters.
  * This is only for experimental queries.
@@ -45,7 +48,10 @@ extensible predicate experimentalSourceModel(
 );
 
 /**
- * DEPRECATED: Do not use.
+ * INTERNAL: Do not use.
+ *
+ * DEPRECATED: This predicate is only intended for adding models used by experimental queries.
+ * This predicate will be deleted in the future.
  *
  * Holds if an experimental sink model exists for the given parameters.
  * This is only for experimental queries.
@@ -56,7 +62,10 @@ extensible predicate experimentalSinkModel(
 );
 
 /**
- * DEPRECATED: Do not use.
+ * INTERNAL: Do not use.
+ *
+ * DEPRECATED: This predicate is only intended for adding models used by experimental queries.
+ * This predicate will be deleted in the future.
  *
  * Holds if an experimental summary model exists for the given parameters.
  * This is only for experimental queries.