chore: retire AREnableSubmitMyCollectionArtworkInSubmitFlow feature flag

[MounirDhahri]

This PR resolves ONYX-1125

Description

This PR retires AREnableSubmitMyCollectionArtworkInSubmitFlow feature flag

PR Checklist

• [x] I have tested my changes on iOS and Android.
• [x] I hid my changes behind a feature flag, or they don't need one.
• [x] I have included screenshots or videos, or I have not changed the UI.
• [x] I have added tests, or my changes don't require any.
• [x] I added an app state migration, or my changes do not require one.
• [x] I have documented any follow-up work that this PR will require, or it does not require any.
• [x] I have added a changelog entry below, or my changes do not require one.

To the reviewers 👀

• [ ] I would like at least one of the reviewers to run this PR on the simulator or device.

Changelog updates

### Changelog updates #### Cross-platform user-facing changes - #### iOS user-facing changes - #### Android user-facing changes - #### Dev changes - retire AREnableSubmitMyCollectionArtworkInSubmitFlow feature flag

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[ArtsyOpenSource]

This PR contains the following changes:

• Dev changes (retire AREnableSubmitMyCollectionArtworkInSubmitFlow feature flag)

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