Remove warning when scikit-learn isn't available.

Most users don't need it.

src/transformers/data/metrics/__init__.py

@@ -14,18 +14,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import logging
-
-
-logger = logging.getLogger(__name__)
-
 try:
     from scipy.stats import pearsonr, spearmanr
     from sklearn.metrics import matthews_corrcoef, f1_score
 
     _has_sklearn = True
 except (AttributeError, ImportError) as e:
-    logger.warning("To use data.metrics please install scikit-learn. See https://scikit-learn.org/stable/index.html")
     _has_sklearn = False