gh-140011: Delete importdl assertion that prevents importing embedded modules from packages

[itamaro]

I still don't know what's the context behind this assertion, just that I didn't see any issues from removing it.

• Issue: Inittab modules in packages hit an assertion since Python 3.13 #140011

[encukou]

It was added in #118204

@ericsnowcurrently, do you remember if there was a reason for this assert?
Can we assume you added asserts when exploring which code paths are taken, and since we had no tests for modules with a dot added via PyImport_AppendInittab, this assert just never fired?

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@itamaro: I'd be a bit more careful in _testembed: from test import create_static_module assumes that the test package is available, which is not always the case. I don't think you'd necessarily want to run testembed without test, but I also don't think we should add an arbitrary requirement/assumption.

Could you add a different containing package to the inittab?