Remove issue template to refer organization settings

[Tiryoh]

Checklists

• [x] I have read the CONTRIBUTING document.
• [x] I have checked to ensure there aren't other open Pull Requests for the same change.

What does this implement/fix? Explain your changes.

このリポジトリ独自のISSUE_TEMPLATEではなくOrganizationで設定してるテンプレートを参照するようにします

Does this close any currently open issues?

いいえ

How has this been tested?

GitHubの設定なのでテストを通していません