chore(ci): use default project from config when deploying to Firebase

Previously, when deploying `scripts/{code,docs}.angularjs.org-firebase/`
to Firebase, we explicitly specified the target projects. Since the
project IDs are also specified in the respective `.firebaserc` files,
this was unnecessary (and meant we had multiple places to update if the
IDs changed).

This commit simplifies the process by automatically targeting the
default projects (as configured in the `.firebaserc` files) when
deploying to Firebase in CI.