Revert "Implement substitution for type variables."

sdk/lib/_internal/compiler/implementation/ssa/nodes.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
diff --git a/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart b/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
index fb12ccb557b1033277ad30aa983a2bfecb0335b3..21b3d713a405df102f31b1002d699d67fd13d4bf 100644
--- a/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
+++ b/sdk/lib/_internal/compiler/implementation/ssa/nodes.dart
@@ -2282,9 +2282,10 @@ class HIs extends HInstruction {
   }
 
   HInstruction get expression => inputs[0];
-  HInstruction get checkCall => inputs[1];
+  HInstruction getCheck(int index) => inputs[index + 1];
+  int get checkCount => inputs.length - 1;
 
-  bool hasArgumentsCheck() => inputs.length > 1;
+  bool hasArgumentChecks() => inputs.length > 1;
 
   HType get guaranteedType => HType.BOOLEAN;