[package-vc] Consider cleaning up files from install process

[Joseph Turner]

package-vc-install currently adds a number of files to a package's
repository which are not tracked by VC.  It is inconvenience to add each
of them to a .gitignore file (or equivalent in other VC systems).  Are
they necessary?  Are you open to removing them in a clean up phase?

For example, when following these instructions to install hyperdrive.el:
https://ushin.org/hyperdrive/hyperdrive-manual.html#package_002dvc

the git repository ends up with these extra untracked files:

dir
hyperdrive-autoloads.el
hyperdrive-pkg.el
hyperdrive.info

Best,

Joseph