[Specs] Remove all the obsolete specs.

sky/specs/frameworks.md

-Frameworks
-----------
-
-Sky is intended to support multiple frameworks. Here is one way you
-could register a custom element using Dart annotations:
-
-```dart
-// @tagname annotation for registering elements
-// only useful when placed on classes that inherit from Element
-class tagname extends AutomaticMetadata {
-  const tagname(this.name);
-  final String name;
-  void init(DeclarationMirror target, Module module, ScriptElement script) {
-    assert(target is ClassMirror);
-    if (!(target as ClassMirror).isSubclassOf(reflectClass(Element)))
-      throw new UnsupportedError('@tagname can only be used on descendants of Element');
-    module.registerElement(name, (target as ClassMirror).reflectedType);
-  }
-}
-```
-
-A framework that used the above code could use the following code to
-get the tag name of an element:
-
-```dart
-String getTagName(Element element) { // O(N) in number of annotations on the class
-  // throws a StateError if the class doesn't have an @tagname annotation
-  var tagnameClass = reflectClass(tagname);
-  return (reflectClass(element.runtimeType).metadata.singleWhere((mirror) => mirror.type == tagnameClass).reflectee as tagname).name;
-}
-```