Fix count of pending submissions involving edits

[ktuite]

Closes getodk/central#561

Submission edits were getting counted/including in pending submissions because their specific submissionDef didn't create any entity defs. I modified the pending submission query to look for any existing entity def with the same submission, not just the same submission def.

What has been done to verify that this works as intended?

Tests

Why is this the best possible solution? Were any other approaches considered?

How does this change affect users? Describe intentional changes to behavior and behavior that could have accidentally been affected by code changes. In other words, what are the regression risks?

Does this change require updates to the API documentation? If so, please update docs/api.md as part of this PR.

no

Before submitting this PR, please make sure you have:

• run make test-full and confirmed all checks still pass OR confirm CircleCI build passes
• verified that any code from external sources are properly credited in comments or that everything is internally sourced