Remove /welcome- command

Deleted /welcome-$conference command because it may or may not work with the change of Discord's ID system and is no longer used.

Discord の ID体系変更に伴って動かなくなるか可能性があり、もう使わないので /welcome-$conference コマンドを削除

minor enhance on mogiri-check

2022.06.04

check all conferences in mogiri-check

Add mogiri-check command

for checking in production

Support multi conferences

for Scrum Fest Niigata / Osaka

welcome-devopsdays command

for admins

add Mocha test

Merge pull request #25 from kawaguti/mocha

Mocha

minor update

Show message if the Eventbrite order ID is for another event.

minor update

Accept Eventbrite order id without "#", if any 10-digits exists

for DevOpsDays Tokyo 2022

Move to Slash Command to follow Discord recommendation
https://discord.com/blog/slash-commands-are-here

minor maintenance

Merge pull request #17 from kawaguti/refactor/clean_legacy

Refactor/clean legacy