Remove ABCSMC.__init__(summary_statistics)

[yannikschaelte]

For major refactoring and the introduction of learned summary statistics, it would make sense to remove this Callable, which in most cases should anyway be an id mapping. Nothing is effectively lost, as the model can just return the "summary statistics / raw data" which are saved in the database. Only problem would be if this feature is used by many applicants. Opinions?

The summary statistics function would then mid-term be replaced by actual summary statistics, which are however not stored in the database, and act differently.