[kernel] Remove references to DispatchCategory

DispatchCategory was removed in 74cf86cb.

Change-Id: Id5fa7710d7cd68d6004360bee90ac342c5f90583
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/273400
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index a7ca404..21726f6 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -2510,8 +2510,7 @@
   /// Indicates whether the implicit setter associated with this field needs to
   /// contain a runtime type check to deal with generic covariance.
   ///
-  /// When `true`, runtime checks may need to be performed; see
-  /// [DispatchCategory] for details.
+  /// When `true`, runtime checks may need to be performed.
   bool get isCovariantByClass => flags & FlagCovariantByClass != 0;
 
   /// Whether the field is declared with the `late` keyword.
@@ -11153,8 +11152,7 @@
   /// whether the method implementation needs to contain a runtime type check to
   /// deal with generic covariance.
   ///
-  /// When `true`, runtime checks may need to be performed; see
-  /// [DispatchCategory] for details.
+  /// When `true`, runtime checks may need to be performed.
   // TODO(johnniwinther): Rename to isCovariantByClass
   bool get isCovariantByClass => flags & FlagCovariantByClass != 0;
 
@@ -13518,8 +13516,7 @@
   /// whether the method implementation needs to contain a runtime type check to
   /// deal with generic covariance.
   ///
-  /// When `true`, runtime checks may need to be performed; see
-  /// [DispatchCategory] for details.
+  /// When `true`, runtime checks may need to be performed.
   bool get isCovariantByClass => flags & FlagCovariantByClass != 0;
 
   void set isCovariantByClass(bool value) {