Suppress NotFound exception when removing reactions for help command
Sentry Issue: [BOT-6X](https://sentry.io/organizations/python-discord/issues/1781203963/?referrer=github_integration)

```
TimeoutError: 
  File "bot/cogs/help.py", line 40, in help_cleanup
    await bot.wait_for("reaction_add", check=check, timeout=300)
  File "asyncio/tasks.py", line 490, in wait_for
    raise exceptions.TimeoutError()

NotFound: 404 Not Found (error code: 10008): Unknown Message
(3 additional frame(s) were not displayed)
...
  File "discord/ext/commands/help.py", line 817, in command_callback
    return await self.send_command_help(cmd)
  File "bot/cogs/help.py", line 203, in send_command_help
    await help_cleanup(self.context.bot, self.context.author, message)
  File "bot/cogs/help.py", line 43, in help_cleanup
    await message.remove_reaction(DELETE_EMOJI, bot.user)
  File "discord/message.py", line 982, in remove_reaction
    await self._state.http.remove_own_reaction(self.channel.id, self.id, emoji)
  File "discord/http.py", line 223, in request
    raise NotFound(r, data)

Error executing command invoked by <REDACTED>: !help purge user
```
diff --git a/bot/cogs/help.py b/bot/cogs/help.py
index 832f6ea6..70e62d59 100644
--- a/bot/cogs/help.py
+++ b/bot/cogs/help.py
@@ -36,13 +36,12 @@ async def help_cleanup(bot: Bot, author: Member, message: Message) -> None:
 
     await message.add_reaction(DELETE_EMOJI)
 
-    try:
-        await bot.wait_for("reaction_add", check=check, timeout=300)
-        await message.delete()
-    except TimeoutError:
-        await message.remove_reaction(DELETE_EMOJI, bot.user)
-    except NotFound:
-        pass
+    with suppress(NotFound):
+        try:
+            await bot.wait_for("reaction_add", check=check, timeout=300)
+            await message.delete()
+        except TimeoutError:
+            await message.remove_reaction(DELETE_EMOJI, bot.user)
 
 
 class HelpQueryNotFound(ValueError):
['bot/cogs/help.py']