我正在用discord.py做一个机器人，我用client.remove_command删除了默认的help cmd，但它不起作用。代码如下：

import discord
from discord.ext import commands

intents = discord.Intents.default()
intents.typing = False
intents.presences = False

client = commands.Bot(command_prefix='!', intents=intents)

@client.event
async def on_ready():
    print('Bot is ready.')

@client.event
async def on_message(message):
    await client.process_commands(message)

@client.event
async def on_command_error(ctx, error):
    if isinstance(error, commands.CommandNotFound):
        await ctx.send('Invalid command.')

# 删除默认的help命令
client.remove_command('help')

@client.command()
async def my_command(ctx):
    await ctx.send('This is my custom command.')

client.run('YOUR_BOT_TOKEN')