remove unused allowConstCast option

lib/src/checker/rules.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dev_compiler.src.checker.rules;
 
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 
@@ skipping 515 matching lines @@
     final Coercion c = _coerceTo(fromT, toT, options.wrapClosures);
     if (c is Identity) return null;
     if (c is CoercionError) return new StaticTypeError(this, expr, toT);
     var reason = null;
     if (options.inferDownwards) {
       var errors = <String>[];
       var ok = inferrer.inferExpression(expr, toT, errors);
       if (ok) return InferredType.create(this, expr, toT);
       reason = (errors.isNotEmpty) ? errors.first : null;
     }
-    if (constContext && !options.allowConstCasts) {
-      reason = (reason == null) ? "Cast not allowed in const context" : reason;
-      return new StaticTypeError(this, expr, toT, reason: reason);
-    }
     if (c is Cast) return DownCast.create(this, expr, c, reason: reason);
     if (c is Wrapper) return ClosureWrap.create(this, expr, c, toT);
     assert(false);
     return null;
   }
 
   DartType elementType(Element e) {
     return (e as dynamic).type;
   }
 
@@ skipping 314 matching lines @@
     var entries = e.entries;
     bool inferEntry(MapLiteralEntry entry) {
       return _inferExpression(entry.key, kType, errors) &&
           _inferExpression(entry.value, vType, errors);
     }
     var b = entries.every(inferEntry);
     if (b) annotateMapLiteral(e, targs);
     return b;
   }
 }