Use remove_device helper in tasmota tests

[epenet]

Proposed change

Follow-up to #116234
Alternative to #116617

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[home-assistant]

Hey there @emontnemery, mind taking a look at this pull request as it has been labeled with an integration (tasmota) you are listed as a code owner for? Thanks!

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[epenet]

I felt it was better to remove this helper method completely, to align with #116240 and #116442

Another possibility is to adjust only this function and have:

    if config_entry_id is None:
        config_entry_id = hass.config_entries.async_entries(DOMAIN)[0].entry_id
    response = await ws_client.remove_device(device_id, config_entry_id)
    assert response["success"]

[epenet]

Alternative created in #116617