Revert "Try to install Salt 3006.8 as test dependency"

Per T2283, it's not currently possible to easily install Salt through pip
to get a suitable environment to run operations tests.

This reverts commit ede81bc373831330abba79fd7e2a9aea01d69e50.

Ref T2283

Reviewed By: yousra

Differential Revision: https://devcentral.nasqueron.org/D4019