Migrate metrics used in flax examples to Evaluate (#18348)

Currently, tensorflow examples use the `load_metric` function from
Datasets library, commit migrates function call to `load` function
from Evaluate library.

examples/flax/token-classification/run_flax_ner.py

@@ -29,9 +29,10 @@ from typing import Any, Callable, Dict, Optional, Tuple
 
 import datasets
 import numpy as np
-from datasets import ClassLabel, load_dataset, load_metric
+from datasets import ClassLabel, load_dataset
 from tqdm import tqdm
 
+import evaluate
 import jax
 import jax.numpy as jnp
 import optax
@@ -646,7 +647,7 @@ def main():
 
     p_eval_step = jax.pmap(eval_step, axis_name="batch")
 
-    metric = load_metric("seqeval")
+    metric = evaluate.load("seqeval")
 
     def get_labels(y_pred, y_true):
         # Transform predictions and references tensos to numpy arrays