remove ensime from IDE.md

[xuwei-k]

Pull Request Checklist

• Have you read How to write the perfect pull request?
• Have you read through the contributor guidelines?
• Have you referenced any issues you're fixing using commit message keywords?
• Have you added copyright headers to new files?
• Have you checked that both Scala and Java APIs are updated?
• Have you updated the documentation for both Scala and Java sections?
• Have you added tests for any changed functionality?

Helpful things

Fixes

Purpose

Background Context

ensime no longer available

• https://github.com/ensime
• https://ensime.github.io/

References

[mkurz]

@Mergifyio backport 2.9.x

[mergify]

backport 2.9.x

✅ Backports have been created

• #12161 [2.9.x] remove ensime from IDE.md (backport #12142) by @xuwei-k has been created for branch 2.9.x