[CLEANUP beta] Fix ember-2-legacy support for Ember.Binding.

The primary change here is to allow `Ember.Mixin.finishPartial` and
`Ember.Mixin.detectBinding` to be undefined/null. The reason for this is
that there is an annoying ordering issue. Basically, the environment
flags are present from when Ember itself boots, but the monkey patches
added by ember-2-legacy (`detectBinding` and `finishPartial`) are not
done until _after_ the main `ember.debug.js` / `ember.prod.js` files
have been processed. _Within_ the evaluation of the main `ember.*.js`
file, the environment variable has been set but these functions are
still missing. This means that _Ember itself_ (during evaluation of
`Ember.CoreObject`) causes an issue when it attempts to call
`Mixin.finishPartials`.

packages/ember-metal/lib/mixin.js

@@ -338,14 +338,14 @@ function applyMixin(obj, mixins, partial) {
       replaceObserversAndListeners(obj, key, obj[key], value);
     }
 
-    if (ENV._ENABLE_BINDING_SUPPORT && Mixin.detectBinding(key)) {
+    if (ENV._ENABLE_BINDING_SUPPORT && typeof Mixin.detectBinding === 'function' && Mixin.detectBinding(key)) {
       meta.writeBindings(key, value);
     }
 
     defineProperty(obj, key, desc, value, meta);
   }
 
-  if (ENV._ENABLE_BINDING_SUPPORT && !partial) { // don't apply to prototype
+  if (ENV._ENABLE_BINDING_SUPPORT && !partial && typeof Mixin.finishProtype === 'function') {
     Mixin.finishPartial(obj, meta);
   }
 

packages/ember-runtime/lib/system/core_object.js

@@ -24,7 +24,6 @@ import {
   Mixin,
   REQUIRED,
   defineProperty,
-  Binding,
   ComputedProperty,
   computed,
   InjectedProperty,
@@ -495,12 +494,6 @@ CoreObject.PrototypeMixin = Mixin.create({
     m.setSourceDestroyed();
   },
 
-  bind(to, from) {
-    if (!(from instanceof Binding)) { from = Binding.from(from); }
-    from.to(to).connect(this);
-    return from;
-  },
-
   /**
     Returns a string representation which attempts to provide more information
     than Javascript's `toString` typically does, in a generic way for all Ember