REF: avoid passing SingleBlockManager to Series
cc @jorisvandenbossche IIRC you didnt want to disallow SingleBlockManager because geopandas passes it.  In those cases, does it also pass `fastpath=True`?  If so, we can consider deprecating allowing SingleBlockManager in the non-fastpath case
I am not fully sure anymore about the context where I would have said that (do you remember the issue/PR?) 
In any case, geopandas handles the case where the `data` passed to the constructor is a SingleBlockManager. And it processes it like kind of a fastpath. But I think geopandas did that rather for compatibility with pandas passing such objects to the constructor, rather than geopandas wanting to pass block managers ourselves (need to check though).

But can you explain a bit in more detail what you propose to change or what you want to achieve? (I don't see much in the diff. You didn't yet change cases that are passing block managers to the constructor?)
 > I am not fully sure anymore about the context where I would have said that (do you remember the issue/PR?)

I think it was in the PR where originally I wanted to make a `_from_mgr` fastpath, which ended up getting folded into `__init__`.

> But can you explain a bit in more detail what you propose to change or what you want to achieve?

After this PR, the check `if isinstance(data, SingleBlockManager)` on L289 is never hit in the tests, so we could disallow it and simplify the constructor. > After this PR, the check if isinstance(data, SingleBlockManager) on L289 is never hit in the tests, so we could disallow it and simplify the constructor.

But that's because the SingleBlockManager is also already handled at L206. 
So you are only speaking about the case of passing SingleBlockManager + other keywords like index/dtype ? I think that is a good idea to disallow/deprecate that.