fix: remove python subscribe demo (#15987)

Co-authored-by: Shuduo Sang <sangshuduo@gmail.com>

docs/examples/python/subscribe_demo.py

-"""
-Python asynchronous subscribe demo.
-run on Linux system with: python3 subscribe_demo.py
-"""
-
-from ctypes import c_void_p
-
-import taos
-import time
-
-
-def query_callback(p_sub, p_result, p_param, code):
-    """
-    :param p_sub: pointer returned by native API -- taos_subscribe
-    :param p_result: pointer to native TAOS_RES
-    :param p_param: None
-    :param code: error code
-    :return: None
-    """
-    print("in callback")
-    result = taos.TaosResult(c_void_p(p_result))
-    # raise exception if error occur
-    result.check_error(code)
-    for row in result.rows_iter():
-        print(row)
-    print(f"{result.row_count} rows consumed.")
-
-
-if __name__ == '__main__':
-    conn = taos.connect()
-    restart = True
-    topic = "topic-meter-current-bg"
-    sql = "select * from power.meters where current > 10"  # Error sql
-    interval = 2000  # consumption interval in microseconds.
-    _ = conn.subscribe(restart, topic, sql, interval, query_callback)
-    # Note: we received the return value as _ above, to avoid the TaosSubscription object to be deleted by gc.
-    while True:
-        time.sleep(10)  # use Ctrl + C to interrupt