Remove outdated model-metadata file when we generate model

[nkylstad]

Description

We no longer persist the model metadata <model>.metadata.json in the app repo, as this is a data structure that we generate as needed.
Apps with existing data models will end up with outdated model metadata files, as an updated file is not generated.
We should therefore remove this file where it exists when a user updates their model and then generates all model files.

Additional Information

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Tasks

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Acceptance Criterias

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[nkylstad]

Tested OK in dev.

Tested with existing app that had the model metadata file:

• ensured that local user was up-to-date with central repo
• added a new field to data model and generated model files
• pushed changes to central repo
  Result: model metadata file was removed.

Tested with existing app that does not have the model metadata file:

• ensured that local user was up-to-date with central repo
• added a new field to data model and generated model files
• pushed changes to central repo
  Result: model generation works as expected with no errors. Model metadata file is not generated, and the fact that it does not exist does not cause any errors with model generation.