Disable riot damage in city (without removing code support)

[moxian]

Summary

None

Purpose of change

This is an alternative to #79580 which effectively reverts the #79535 changes as far as user experience goes, but leaves the code support in so that it can be further worked on behind the curtains until it's in better shape (see #79584 and #79575)

tagging #79565, although this does not technically fix the core issue

Describe the solution

JSON-only change. With this PR no overmap has PP_GENERATE_RIOT_DAMAGE flag so the riot damage generator never runs.
But it can still be enabled locally for testing very easily.

Describe alternatives you've considered

Completely revert the code as #79580 does. That would be preferable if this feature is fundamentally unfixable (since the current PR effectively creates dead code, and having dead code is not ideal)

Testing

Additional context

[GuardianDll]

#79575 resolved the error, so i do not see a reason to remove generator anymore