chore(config): remove upgrade package mappings

The package is not listed in `package.json` and angular/angular.io#2803 will contain instructions to add it manually.

Author: filipesilva

systemjs.config.js

@@ -23,8 +23,6 @@
       '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
       '@angular/router/upgrade': 'npm:@angular/router/bundles/router-upgrade.umd.js',
       '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',
-      '@angular/upgrade': 'npm:@angular/upgrade/bundles/upgrade.umd.js',
-      '@angular/upgrade/static': 'npm:@angular/upgrade/bundles/upgrade-static.umd.js',
 
       // other libraries
       'rxjs':                      'npm:rxjs',