Cleanup PdfJsTelemetry addon stub

[georgf]

This is a follow-up to #8239, renaming the PdfJsTelemetry-addon.jsm file and removing left-overs.

[Snuffleupagus]

Unless I'm mistaken, it looks like the old extensions/firefox/content/PdfJsTelemetry-addon.jsm file isn't actually being removed in this PR (only a new file is added). Hence I'd suggest using the git mv command to rename the existing file, since this has the added bonus of retaining the commit history for the file.

[georgf]

I used git mv, is anything broken?

[Snuffleupagus]

I used git mv, is anything broken?

Well, not "broken" as such, but as mentioned it looks like the old PdfJsTelemetry-addon.jsm file isn't actually being removed in the patch!?

[timvandermeij]

Indeed, something appears to have gone wrong. If you look at the diff at https://github.com/mozilla/pdf.js/pull/8254/files, PdfJsTelemetry-stub.jsm is created, but PdfJsTelemetry-addon.jsm still exists as well, while that one should have been removed.

[Snuffleupagus]

Landed in PR #8275 (obviously keeping the author information correct), thank you for the patch!