Fix gradle error hints.

gradle/generation/javacc.gradle

@@ -269,6 +269,8 @@ class JavaCCTask extends DefaultTask {
    * Apply closures to all generated files before they're copied back
    * to mainline code.
    */
+  // A subtle bug here is that this makes it not an input... should be a list of replacements instead?
+  @Internal
   List<Closure<FileTree>> afterGenerate = new ArrayList<>()
 
   @OutputFiles

gradle/generation/jflex.gradle

@@ -222,7 +222,7 @@ class JFlexTask extends DefaultTask {
   @InputFile
   File skeleton
 
-  @Optional
+  @Internal
   String heapSize
 
   @OutputFile