Added deletion of unused commands

[spinnerich]

Description

Added the possibility to delete commands which are not used by the bot but are still registered to the Discord API.

Usage

Normal usage:

from discord.ext import commands
from discord_slash import SlashCommand
bot = commands.Bot(command_prefix="!", intents=discord.Intents.all())

slash = SlashCommand(bot, auto_delete=True) # Auto delete at startup
await slash.delete_unused_commands() # Cleanup at a later point

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

[4surix]

It's a good idea !
I think it's better than my function to delete all the commands #41 (well maybe some people will have the use of my function) but your function is more like what I wanted to do.

[eunwoo1104]

First of all, sorry for the edit thing, I accidentally clicked the wrong one.
Merging this pull request. Thank you for contributing!