[BUG] in sample: linkedin-auth: depends on "node-linkedin" library which has been broken for 2 years

### Which sample has a bug?

linkedin-auth

### How to reproduce the issue

Trying to follow the sample as-is hits a bug fixed by https://github.com/firebase/functions-samples/pull/826 . If you apply that PR, then you get a crash in the function `exports.token` in `functions/index.js`. The crash can ultimately be traced to the fact that the sample uses the library `node-linkedin`, which relies for getting user profile data on an API that LinkedIn has stopped providing almost 2 years ago, on May 1 2019:
https://github.com/ArkeologeN/node-linkedin/issues/88

The sample needs to be changed to use an up to date library. I haven't found a replacement library I'm comfortable using yet though.