docs(downloading.ngdoc): remove link to Google CDN overview page
docs(downloading.ngdoc): remove link to Google CDN overview page

AngularJS is no longer listed on the CDN page, because the available versions
were almost always out of date due to the need to manually update the list

angular/angular.js,eistrati/angular.js,Narretz/angular.js,gkalpak/angular.js,mosoft521/angular.js,mgol/angular.js,jbedard/angular.js,reneploetz/angular.js,mosoft521/angular.js,Narretz/angular.js,jbedard/angular.js,mgol/angular.js,mosoft521/angular.js,ze-pequeno/angular.js,angular/angular.js,mgol/angular.js,reneploetz/angular.js,jbedard/angular.js,angular/angular.js,angular/angular.js,gkalpak/angular.js,mgol/angular.js,reneploetz/angular.js,ze-pequeno/angular.js,reneploetz/angular.js,ze-pequeno/angular.js,mosoft521/angular.js,gkalpak/angular.js,Narretz/angular.js,eistrati/angular.js,eistrati/angular.js,gkalpak/angular.js,jbedard/angular.js,eistrati/angular.js,ze-pequeno/angular.js,Narretz/angular.js