refactor(store): move rollback_test.go to tests/integration

[kocubinski]

Description

Required for #13110, and is the last reference to simapp outside of tests/. This is an integration test as written, so I've moved it to tests/integration. Had I refactored to depend on x/modules instead of simapp I'd have introduced new dependencies in store on x/ which aren't there now. Therefore keeping the test as-is and moving it makes the most sense to me.

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