Release 2.28.1 to Fedora (RH#1495852)
- Drop userd backport patches, they are part of 2.28 release
- Backport changes to rework distro checks to fix derivative distro usage of snapd
- Revert import path change for cheggaaa/pb as it breaks build on Fedora
- Add a posttrans relabel to snapd-selinux to ensure everything is labeled correctly