TST/CLN: empty DataFrames and some 'empty' Series
xref https://github.com/pandas-dev/pandas/pull/24886#issuecomment-468984081

have included Series constructed with an empty dict.

Series constructed with an empty list, tuple or generator are not the same as Series() or Series({}), so have not included them in this pass. (although for many tests the difference in the Index is not relevant) 
