chore: Revert "feat(backend): support single phase transfer in connector"

[mkurapov]

This reverts commit 81f8a059229d4d8e1ce714cf12605f5a17d127d3.

Changes proposed in this pull request

• Reverting commit that introduced single phase transfers: we ended up having an issue of incoming payments not being able to complete, more details in #2629
• Adding to integration test to make sure this case is tested

Context

Progress towards fixing #2629

Checklist

• [x] Related issues linked using fixes #number
• [x] Tests added/updated
• [ ] Documentation added
• [ ] Make sure that all checks pass
• [ ] Bruno collection updated

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