Do not trim indexes

[grzesiek2010]

Closes #3126

It is a continuation of getodk/javarosa#469

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

I tested the attached form.

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

It just removes redundant functionality. it is redundant because of getodk/javarosa#469

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?

getodk/javarosa#469 with this pr should just fix the issue and nothing else. Testing indexes visible in the audit file would be enough.

Do we need any specific form for testing your changes? If so, please attach one.

I used this one:
test.xml.txt
but any form with regular groups and repeatable groups is fine.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

No, I thought that we have some samples in the doc that we would need to fix but looks as if I was wrong.

Before submitting this PR, please make sure you have:

• run ./gradlew checkAll and confirmed all checks still pass OR confirm CircleCI build passes and run ./gradlew connectedDebugAndroidTest locally.
• verified that any code or assets from external sources are properly credited in comments and/or in the about file.
• verified that any new UI elements use theme colors. UI Components Style guidelines

[lognaturel]

Commit cherry-picked into #3231