realm/playground: Add API endpoint for deleting a playground entry.

Similar to the previous commit, we have added a `do_*` function
which does the deletion from the DB. The next commit handles sending
the events when both adding and deleting a playground entry.

Added the openAPI format data to zulip.yaml for DELETE
/realm/playgrounds/{playground_id}. Also added python and curl
examples to remove-playground.md.

Tests added.

zerver/openapi/curl_param_value_generators.py

@@ -14,6 +14,7 @@ from django.utils.timezone import now as timezone_now
 from zerver.lib.actions import (
     do_add_linkifier,
     do_add_reaction,
+    do_add_realm_playground,
     do_create_user,
     update_user_presence,
 )
@@ -277,6 +278,19 @@ def add_realm_playground() -> Dict[str, object]:
     }
 
 
+@openapi_param_value_generator(["/realm/playgrounds/{playground_id}:delete"])
+def remove_realm_playground() -> Dict[str, object]:
+    playground_info = dict(
+        name="Python playground",
+        pygments_language="Python",
+        url_prefix="https://python.example.com",
+    )
+    playground_id = do_add_realm_playground(get_realm("zulip"), **playground_info)
+    return {
+        "playground_id": playground_id,
+    }
+
+
 @openapi_param_value_generator(["/users/{user_id}:delete"])
 def deactivate_user() -> Dict[str, object]:
     user_profile = do_create_user(