[Bug]: Unused binds in TestDataModule

### Is there an existing issue for this?

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### What happened?

There are some repository binds in TestDataModule that are not provided or injected anywhere in the app, so you've got some FakeRepository classes sitting idle e.g FakeTopicsRepository

Instead, you are using test doubles data sources e.g TestNiaNetworkDataSource where you create a fake data source e.g FakeNiaNetworkDataSource from the network module.

`package com.google.samples.apps.nowinandroid.core.data.test.TestDataModule`

Thanks
Patryk

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