Don't specify flavors for Leap 15.4 appliances

[lkocman]

• All JeOS images were renamed to MinimalVM
• same as Leap 15.5

Fixes

mirror@pontifex2:~/openSUSE-release-tools> ./publish_distro publish_distro_conf/publish_leap154_appliances.config 
kvm-and-xen with * doesn't exist, skipping isos
nothing to do

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (178896c) 28.45% compared to head (1b9dce0) 28.45%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3001 +/- ## ======================================= Coverage 28.45% 28.45% ======================================= Files 85 85 Lines 14716 14716 ======================================= Hits 4188 4188 Misses 10528 10528 ```

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