Remove filesystem token for Brew. Use crendential plugin

[j-rivero]

The PR removes the injection of the GITHUB token into jenkins-scripts/lib/_homebrew_github_setup.bash to work using the same variable injected via credentials plugin. @scpeters if you please find a chance to test it, appreciated.

[scpeters]

the DSL modifies 2 jobs:

• generic-release-homebrew_pull_request_updater for opening homebrew-simulation pull requests
• generic-release-homebrew_pr_bottle_hash_updater for updating the bottle hashes after successfully building and uploading bottles

I'll test these two jobs separately

[scpeters]

• generic-release-homebrew_pull_request_updater for opening homebrew-simulation pull requests

this is easy to test; I'll just rerun the following job with this branch after deploying the DSL from this branch. I expect it to open a pull request to revert sdformat 15.1.1 back to sdformat 15.1.0 (I won't merge it). If it pushes a branch and opens a pull request, then it counts as a success

• https://build.osrfoundation.org/job/generic-release-homebrew_pull_request_updater/1598/

[scpeters]

• generic-release-homebrew_pull_request_updater for opening homebrew-simulation pull requests

this is easy to test; I'll just rerun the following job with this branch after deploying the DSL from this branch. I expect it to open a pull request to revert sdformat 15.1.1 back to sdformat 15.1.0 (I won't merge it). If it pushes a branch and opens a pull request, then it counts as a success

deploying DSL: https://build.osrfoundation.org/job/_dsl_brew_release/938/

running generic-release-homebrew_pull_request_updater: https://build.osrfoundation.org/job/generic-release-homebrew_pull_request_updater/1608/

[scpeters]

If it pushes a branch and opens a pull request, then it counts as a success

deploying DSL: https://build.osrfoundation.org/job/_dsl_brew_release/938/

running generic-release-homebrew_pull_request_updater: https://build.osrfoundation.org/job/generic-release-homebrew_pull_request_updater/1608/

success! osrf/homebrew-simulation#2891

[scpeters]

the code paths are the same between the two jobs, so I'm comfortable approving after that test

[j-rivero]

Great! Thanks so much for doing the test. One credential less!