remove undefined action reference X_RefreshFromSnapshotsListAndActions

[c-hartmann]

.desktop source still references a planned but never implemented action reference
'X_RefreshFromSnapshotsListAndActions',
that has been silently ignored in Plasma 5, but not Plasma 6 and leads to an empty
context menu item when used therein.

so far, this has no impact on it's functionality, but just looks bad. so remove it, as there
are no further plans on implementing an unimplementable or at least just dirty
implementable thing.