Remove Implicit NumPy Conversion in BaseSearchCV (#849)

[ChadGueli]

This pull removes a call to delayed which implicitly converted Dask Arrays to NumPy. Since Delayed objects are hash-able, unlike Arrays, id is called on Dask Array to get hashable values.

There is a twin issue with implicit conversion of Dask DataFrames to Pandas, unfortunately that issue is harder to fix because Dask DataFrames do not permit integer-based row indexing.