clients: fix references to bookstore and non-existent files

[broady]

examples/swagger/bookstore/swagger-firebase.json

These should point toward the Echo samples' swagger.yaml

[broady]

All of these need fixing:

$ git grep bookst
firebase-android/README.md:[examples/swagger/bookstore/swagger-firebase.json](/examples/swagger/bookstore/swagger-firebase.json)
firebase-android/README.md:example, the [Node.js Bookstore example](/examples/nodejs/bookstore) backend is
firebase-android/app/src/facebook/java/com/google/firebase/quickstart/auth/FacebookLoginActivity.java:            "https://endpoints-bookstore-node.appspot.com/shelves/1";
firebase-android/app/src/main/java/com/google/firebase/quickstart/auth/GoogleSignInActivity.java:            "https://endpoints-bookstore-node.appspot.com/shelves/1";
firebase-ios/AuthenticationExample/Info.plist:  <string>https://endpoints-bookstore-node.appspot.com/shelves/1</string>
firebase-ios/README.md:[examples/swagger/bookstore/swagger-firebase.json](/examples/swagger/bookstore/swagger-firebase.json)
firebase-ios/README.md:example, the [Node.js Bookstore example](/examples/nodejs/bookstore) backend is
firebase-js/README.md:[examples/swagger/bookstore/swagger-firebase.json](/examples/swagger/bookstore/swagger-firebase.json)
firebase-js/README.md:example, the [Node.js Bookstore example](/examples/nodejs/bookstore) backend is
firebase-js/google-redirect.html:    var ENDPOINTS_URL = 'https://endpoints-bookstore-node.appspot.com/shelves/1';
google-js/README.md:Start Google Cloud Endpoints and the bookstore backend. The whole API surface,
google-js/README.md:[examples/swagger/bookstore/swagger-google-id-token.json](/examples/swagger/bookstore/swagger-google-id-token.json).
google-js/index.html:            url: "https://endpoints-bookstore-node.appspot.com/shelves/1",