refactor: Remove functions_background_synchronous

[grant]

Removes functions_background_synchronous.
This sample do not show any new feature that is not shown in other samples.
It is also is not a useful sample to duplicate across languages.

Docs: https://cloud.google.com/functions/docs/writing/background#terminating_background_functions
CL: cl/270366828

[ace-n]

Not a bad idea, but can you update the relevant doc first?

[grant]

Not a bad idea, but can you update the relevant doc first?

I've created CL 270366828. Note, I'm not able to stage due to updates to Devsite 2.

[ace-n]

LGTM if @labtopia approves the docs changes.

[grant]

The error states:

  ✓ should make a promise request (498ms)
  functions_background_synchronous
    1) should return synchronously
    ✓ should throw an error


  2 passing (2s)
  1 failing

  1) functions_background_synchronous
       should return synchronously:
     TypeError: program.helloSynchronous is not a function
      at Context.it (test/index.test.js:73:15)

But this has been removed. Not sure what is happening.

[grant]

The broken test is completely separate from the changes made in this PR.

Internal CI (run/logging-manual) — Tests failed.

It's not in the functions/ directory.

Since this PR is approved and functions/ test pass, merging.