remotes 2.4.1

• pkgbuild is no longer accidentally loaded even in standalone mode (#548)
• The internal GitHub token used to increase rate limits has been regenerated.
• Using remote_package_name.git2r_remote now passes credentials when looking up the package DESCRIPTION (#633, @rnorberg)
• Using remote_package_name.git2r_remote and remote_package_name.xgit_remote, http responses returning an invalid DESCRIPTION or that redirect to another page will now fallback to return NA instead of throwing an error when trying to parse the unexpected content (#628, @dgkf).
• Fix regex that breaks git protocol in git_remote (@niheaven #630).
• Clarify github_pull() documentation (@ms609 #640).