Prevent deserialization problem with Espionage

[SomeTroglodyte]

There was an issue where I commented on this, but can't find it.
With current master, no save can be reloaded that has a non-empty erasSpyEarnedFor.

• Too much comment?
• Sniffing into Espionage - I would be tempted to allow unique quotes and portraits per individual Spy, at least as Mod. Imagine a mugshot taken from wikipedia plus the quote "A harlot? Yes, but a traitoress, never! - Phrase attributed to margaretha Zelle during the trial" for "Mata Hari"...
  Civ5 itself seem not to have such a feature... Yes/No, and if Yes - data schema? Extra Json, mapping decorations per Spy name / deprecate spyNames in favour of an array of SpyMetadata objects / custom deserializer that reads both? Display on-click in Espionage screen or on getting a Spy as AlertPopup like the Tech/Wonder quotes?

[yairm210]

Yeah you're commenting why you make the change, but the next dev who comes will be like 'why is it taking about mutableSetOf if it doesn't appear anywhere?"

[SomeTroglodyte]

I thought that read "do not use..." But then maybe the whole comment should go on IsPartOfGameInfoSerialization instead..