(chore): Delete stale.yml

[hubertdeng123]

This logic for marking issues as stale is now moved to eng-pipes so it's easier to change the logic instead of going through all stale.yml files across Sentry.

https://github.com/getsentry/eng-pipes/blob/3236a12d691c4bf26721b3aad95cc247daad3813/src/webhooks/pubsub/stalebot.ts

[github-actions]

	Fails
🚫	Please consider adding a changelog entry for the next release.

Instructions and example for changelog

Please add an entry to CHANGELOG.md to the "Unreleased" section. Make sure the entry includes this PR's number.

Example:

## Unreleased

- Delete stale.yml ([#2069](https://github.com/getsentry/sentry-ruby/pull/2069))

If none of the above apply, you can opt out of this check by adding #skip-changelog to the PR description.

Generated by 🚫 dangerJS against 5b2813d

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.02 ⚠️

Comparison is base (e31cc77) 83.24% compared to head (5b2813d) 83.23%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2069      +/-   ##
==========================================
- Coverage   83.24%   83.23%   -0.02%     
==========================================
  Files         119      119              
  Lines        5665     5665              
==========================================
- Hits         4716     4715       -1     
- Misses        949      950       +1     

see 1 file with indirect coverage changes

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