Drop FKs referencing DomainHistory

[gbrodman]

• We never delete rows from DomainHistory (and even if we do in the future, they'll be old / the references won't matter)
• This is likely creating lock contention when lots of requests come through at once for domains with many DomainHistory entries

We add them as indexes just in case

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This change is 

[jianglai]

I'm curious how you arrived at these files with no change in the Java file to drop the fk constraint AFAICT. Did you do this manually?

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[gbrodman]

Yes, I did this manually (except for the generated SQL file obviously). All of the foreign keys that we're removing in this PR, except for GracePeriodHistory, were created manually in the first place since the generated code only generates foreign keys when one object (in this case DomainHistory) stores another (in this case GracePeriodHistory).

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @CydeWeys)

[jianglai]

Good to know, thanks.

Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @CydeWeys)