Remove obsolete pdfjs-dist code from the Gulpfile

[timvandermeij]

The Git logic for pushing to the pdfjs-dist repository was already removed in PR #18350, but it was forgotten to also remove the logic to create a Git repository in the first place. This commit fixes the open action for that from
#18358 (comment).

Moreover, we implement the suggestion from #18358 (comment) about moving the Git URL to a separate variable for consistency and we update the homepage URL to the HTTPS scheme to avoid an HTTP -> HTTPS redirect and enforce TLS-encrypted connections.

Fixes #18357. Once this is approved and merged, we can archive the pdfjs-dist repository.

[timvandermeij]

I have diffed the contents of the old and new build/dist directory and confirmed that in the new version the .git directory is gone and no other relevant changes to files were made (the only changes were due to the Git hash, and therefore the build number, changing between the branches).

I have also diffed the contents of the NPM publish command, in dry-run mode, that we use the publish release workflow. I used the following set of commands:

$ npm publish ./build-old/dist --provenance --dry-run | tee old.log
$ npm publish ./build-new/dist --provenance --dry-run | tee new.log
$ diff old.log new.log 
1c1
< + [email protected]
---
> + [email protected]

Note that also here the only change is the build number due to the extra commit on the new branch, but more importantly the list of files that are part of the release tarball has no changes.

[Snuffleupagus]

r=me, thank you!