[ML] Delete 90903 change log entry (#91054)

As #90903 made the cut for `8.5.0`, the issue
is no longer a bug. After udpating the PR to `non-issue`,
this commit also deletes the release note from the changelog.

docs/changelog/90903.yaml

@@ -1,5 +0,0 @@
-pr: 90903
-summary: Require correct tier processors when multiple AZs are present
-area: Machine Learning
-type: bug
-issues: []