Bug 1731145: Don't ignore vendored package `*.egg-info` directories r=ahal

The `*.egg-info` directories are needed for the packages to show up as
"distributions" to `pip` and other environment-checking logic.

We know that `*.egg-info` directories are cross-platform because they
exist in the globally-usable `tar.gz` releases of packages.

Differential Revision: https://phabricator.services.mozilla.com/D125909