Remove disable_sync_subtasks from the EagerResult.get method.

[YPCrumble]

Fixes #6072.

@auvipy this draft is what I was suggesting for EagerResult. Because the task is run "locally" it means that the issues with synchronous subtasks should not apply. For instance, the docs suggest that this "may even cause a deadlock if the worker pool is exhausted", but because an EagerResult created by apply is not sent to the worker pool this isn't possible.

I suppose there's a chance that EagerResult could potentially be created somewhere other than the apply function, but I couldn't find an instance of this in the code to date. As long as EagerResult is never a result of a task generated by the worker pool I think this PR makes sense, because there is no chance of deadlock.

If this PR makes sense I would be happy to update the docs and warnings, as well as improve the docstrings.

Thanks again for maintaining Celery, and I'd love to hear your feedback on this PR!

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Description

[auvipy]

demonstrating a failing test case, along with the proposed removal of disable_sync_subtasks check is needed to properly understand the scenario