dart2js cps: Fix some analyzer hints in the CPS backend.

pkg/compiler/lib/src/cps_ir/bounds_checker.dart

Index: pkg/compiler/lib/src/cps_ir/bounds_checker.dart
diff --git a/pkg/compiler/lib/src/cps_ir/bounds_checker.dart b/pkg/compiler/lib/src/cps_ir/bounds_checker.dart
index 223c24a303c8f3b52a87fcabdfc83e228c1206f1..44cbbb0e010ad425164794eefba72aa42dd37b0c 100644
--- a/pkg/compiler/lib/src/cps_ir/bounds_checker.dart
+++ b/pkg/compiler/lib/src/cps_ir/bounds_checker.dart
@@ -493,7 +493,6 @@ class BoundsChecker extends TrampolineRecursiveVisitor implements Pass {
   void visitBoundsCheck(BoundsCheck node) {
     if (node.checks == BoundsCheck.NONE) return;
     assert(node.index != null); // Because there is at least one check.
-    Primitive object = node.object.definition;
     SignedVariable length = node.length == null
         ? null
         : getValue(node.length.definition);