Revert "Constant fold charCodeAt via constant system"

sdk/lib/_internal/compiler/implementation/constant_system_dart.dart

Index: sdk/lib/_internal/compiler/implementation/constant_system_dart.dart
diff --git a/sdk/lib/_internal/compiler/implementation/constant_system_dart.dart b/sdk/lib/_internal/compiler/implementation/constant_system_dart.dart
index d800d6dd30f8e3dbe4407afa5984dbd2b3c672e1..624d967e47ee75dd93ba0217fce0ef113471d04a 100644
--- a/sdk/lib/_internal/compiler/implementation/constant_system_dart.dart
+++ b/sdk/lib/_internal/compiler/implementation/constant_system_dart.dart
@@ -318,35 +318,6 @@ class IdentityOperation implements BinaryOperation {
   apply(left, right) => identical(left, right);
 }
 
-abstract class CodeUnitAtOperation implements BinaryOperation {
-  final String name = 'charCodeAt';
-  const CodeUnitAtOperation();
-  apply(left, right) => left.codeUnitAt(right);
-}
-
-class CodeUnitAtConstantOperation extends CodeUnitAtOperation {
-  const CodeUnitAtConstantOperation();
-  ConstantValue fold(ConstantValue left, ConstantValue right) {
-    // 'a'.codeUnitAt(0) is not a constant expression.
-    return null;
-  }
-}
-
-class CodeUnitAtRuntimeOperation extends CodeUnitAtOperation {
-  const CodeUnitAtRuntimeOperation();
-  IntConstantValue fold(ConstantValue left, ConstantValue right) {
-    if (left.isString && right.isInt) {
-      DartString dartString = left.primitiveValue;
-      int index = right.primitiveValue;
-      if (index < 0 || index >= dartString.length) return null;
-      String string = dartString.slowToString();
-      int value = string.codeUnitAt(index);
-      return DART_CONSTANT_SYSTEM.createInt(value);
-    }
-    return null;
-  }
-}
-
 /**
  * A constant system implementing the Dart semantics. This system relies on
  * the underlying runtime-system. That is, if dart2js is run in an environment
@@ -376,7 +347,6 @@ class DartConstantSystem extends ConstantSystem {
   final shiftRight = const ShiftRightOperation();
   final subtract = const SubtractOperation();
   final truncatingDivide = const TruncatingDivideOperation();
-  final codeUnitAt = const CodeUnitAtConstantOperation();
 
   const DartConstantSystem();