Remove hack from KernelTypePromoter.isPromotionCandidate.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
index fdf482503c6d6125677133de2e8af656b6911e17..d47684145b24c2f64a4905fab7531f62faed53f8 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart
@@ -2134,15 +2134,9 @@ class KernelTypePromoter extends TypePromoterImpl {
 
   @override
   bool isPromotionCandidate(VariableDeclaration variable) {
-    if (variable is KernelVariableDeclaration) {
-      return !variable._isLocalFunction;
-    } else {
-      // Hack to deal with the fact that BodyBuilder still creates raw
-      // VariableDeclaration objects sometimes.
-      // TODO(paulberry): get rid of this once the type parameter is
-      // KernelVariableDeclaration.
-      return true;
-    }
+    assert(variable is KernelVariableDeclaration);
+    KernelVariableDeclaration kernelVariableDeclaration = variable;
+    return !kernelVariableDeclaration._isLocalFunction;
   }
 
   @override