[BUG] [Package Tests] MacOS installers don't keep salt-pip extras directory in previous state

[MKLeb]

Description
When upgrading or downgrading relenv macos packages, the extras-X.Y directory is reset to being empty.

Once fixed, the downgrade tests should be altered to test that this is working correctly in test_salt_downgrade.py.

Setup

• on-prem machine
• VM (Virtualbox, KVM, etc. please specify)
• VM running on a cloud service, please be explicit and add details
  • Parallels
• container (Kubernetes, Docker, containerd, etc. please specify)
• or a combination, please be explicit
• jails if it is FreeBSD
• classic packaging
• onedir packaging
• used bootstrap to install

Steps to Reproduce the behavior

• Install v3006.1
• salt-pip install pep8
• Notice that the installed pep8 package is in extras-X.Y
• Install v3006.2
• Notice that pep8 is no longer present in any fashion in extras-X.Y

Expected behavior
The extras directory should still have the installed pep8 package