Delete .github/ISSUE_TEMPLATE directory

[ryanwilson]

Description of the change

Remove the issue templates in this repo in order to use the org's issue templates.

Motivation

This will now use the issue templates at the base of the google-gemini organization instead.

Type of change

Documentation

Checklist

• I have performed a self-review of my code.
• I have added detailed comments to my code where applicable.
• I have verified that my change does not break existing code.
• My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• I am familiar with the Google Style Guide for the language I have coded in.
• I have read through the Contributing Guide and signed the Contributor License Agreement.