[infra] Remove Linux NUC9i7QN tasks

All of the machines to run these have died.

Change-Id: Ieaa53678e451faec315dac5baee009cd236f56ab
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/919076
Auto-Submit: Eric Boren <borenet@google.com>
Reviewed-by: Kaylee Lubick <kjlubick@google.com>