chore(compiler): remove unused, expired code

Author: matsko

lib/core_dom/compiler.dart

@@ -176,10 +176,9 @@ class Compiler {
           mappingFn = (NodeAttrs attrs, Scope scope, Object dst) {
             if (attrs[attrName] == null) return;
             Expression attrExprFn = _parser(attrs[attrName]);
-            var shadowValue = null;
             scope.$watch(
                     () => attrExprFn.eval(scope),
-                    (v) => dstPathFn.assign(dst, shadowValue = v),
+                    (v) => dstPathFn.assign(dst, v),
                     attrs[attrName]);
           };
           break;