fix(plugins): removed unnecessary es5 helper support

BREAKING CHANGE: If you were using ES5 and used the computed helper on
function, this will affect you as that is no longer present.

src/plugins.js

@@ -63,24 +63,6 @@ export class Plugins {
     return this;
   }
 
-  /**
-   * Installs special support for ES5 authoring.
-   *
-   * @method es5
-   * @return {Plugins} Returns the current Plugins instance.
- */
-  es5(){
-    Function.prototype.computed = function(computedProperties){
-      for(var key in computedProperties){
-        if(computedProperties.hasOwnProperty(key)){
-          Object.defineProperty(this.prototype, key, { get: computedProperties[key], enumerable: true });
-        }
-      }
-    };
-
-    return this;
-  }
-
   _process(){
     var aurelia = this.aurelia,
         loader = aurelia.loader,

test/plugin.spec.js

@@ -118,29 +118,5 @@ describe('the plugin loader', () => {
         done();
       });
     });
-
-
-  });
-
-  describe("es5()", () => {
-    afterEach(() => Function.prototype.computed = undefined);
-
-    it("adds the computed function on the Function prototype", () => {
-      expect(Function.prototype.computed).toBeUndefined();
-      plugins.es5();
-      expect(Function.prototype.computed).toEqual(jasmine.any(Function));
-    });
-
-    it("Function.prototype.computed adds read only object keys to a function", () => {
-      plugins.es5();
-      function TestFn() {}
-
-      var metaData = {intProp: () => 1, boolProp: () => false};
-      TestFn.computed(metaData);
-      var testFn = new TestFn();
-
-      expect(testFn.intProp).toBe(1);
-      expect(testFn.boolProp).toBeFalsy();
-    });
   });
 });