apacheGH-36243: [Dev] Remove PR workflow label as part of merge

dev/merge_arrow_pr.py

@@ -421,8 +421,19 @@ def merge_pr(self, number, commit_title, commit_message):
         if response.status_code != 200 and 'merged' not in result:
             result['merged'] = False
             result['message'] += f': {url}'
+        else:
+            self.clear_pr_state_labels(number)
         return result
 
+    def clear_pr_state_labels(self, number):
+        url = f'{self.github_api}/issues/{number}/labels'
+        response = requests.get(url, headers=self.headers)
+        labels = response.json()
+        for label in labels:
+            if label['name'].startswith('awaiting'):
+                label_url = f"{url}/{label['name']}"
+                response = requests.delete(label_url, headers=self.headers)
+
 
 class CommandInput(object):
     """