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/question-answering/run_qa.py

@@ -32,9 +32,10 @@ from typing import Any, Callable, Dict, Optional, Tuple
 
 import datasets
 import numpy as np
-from datasets import load_dataset, load_metric
+from datasets import load_dataset
 from tqdm import tqdm
 
+import evaluate
 import jax
 import jax.numpy as jnp
 import optax
@@ -776,7 +777,7 @@ def main():
         references = [{"id": ex["id"], "answers": ex[answer_column_name]} for ex in examples]
         return EvalPrediction(predictions=formatted_predictions, label_ids=references)
 
-    metric = load_metric("squad_v2" if data_args.version_2_with_negative else "squad")
+    metric = evaluate.load("squad_v2" if data_args.version_2_with_negative else "squad")
 
     def compute_metrics(p: EvalPrediction):
         return metric.compute(predictions=p.predictions, references=p.label_ids)