Remove dependency in language_content_settings and improve tests

Problem/Motivation

While looking at the language_content_settings migrations in response to #2936636: General migration issues from D6 ubercart with multiple languages I noticed that there was a dependency added that could be removed and the test was not robust enough.

Marking a bug report since the tests are not doing what is should.

Proposed resolution

Remove the dependency set in the alter.
It would be better if there were 2 tests, one executing d6_language_content_settings, and the other executing, d6_language_content_settings and d6_ubercart_language_content_settings. Since both are modified in an alter, it makes sense to test that the core migration doesn't modify the products and that the combination of both, does what it should in a complete migration.

Update the test to correctly test for translatability as per the test in core.

Remaining tasks

Write a patch
review
commit
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