[MergeDups] Improve protection-override data-loss warning

[imnasnainaec]

When overriding word/sense protection, if you move a protected sense to a different word and it was the last sense in a protected word, a warning pops up listing what things will be lost. It lists things for both the word and sense even though the sense is just being moved. We only need the warning to include the sense details if the sense is being deleted, merged into another sense, or displaced from the top of the sidebar.