Fix a comment

Author: jcollins-g

lib/src/model.dart

@@ -3805,8 +3805,8 @@ class Package extends Canonicalization with Nameable, Warnable {
 
   /// Returns true if there's at least one library documented in the package
   /// that has the same package path as the library for the given element.
-  /// Usable as a cross-check for dartdoc's canonicalization -- if we're
-  /// generating a link to something
+  /// Usable as a cross-check for dartdoc's canonicalization to generate
+  /// warnings for ModelElement.isPublicAndPackageDocumented.
   Set<String> _allRootDirs;
   bool packageDocumentedFor(ModelElement element) {
     if (_allRootDirs == null) {