[MRG+1] Raise error when SparseSeries is passed into classification metrics (#7373)

* Raise error when SparseSeries is passed into roc_curve

* Changed "y_true" in second if block to "y_score"

* Remove code to import pandas and add sparseseries check to 'type_of_target' function. Finally, add 'type_of_target' call to _binary_clf_curve

* Remove pandas import and old comparison in roc_curve.

* Add test for 'type_of_target' function

* Add white space after commas

* Correct other white space issues

* Move type_of_target test into try clause, remove test_precision_recall_curve_pos_label since as multiclass it doesn't make sense

* Add test_precision_recall_curve_pos_label back in and also add test_binary_clf_curve to test new logic in _binary_clf_curve function

* Correct syntax and formatting.

* Remove trailing white space

* Correct validation logic

* Update test_multiclass.py per @jnothman 's request.

* Import SkipTest function.

* Remove extra white space from line 303