Revert "[infra] Update checked-in SDKs to 2.9.0-10.0.dev"
Revert "[infra] Update checked-in SDKs to 2.9.0-10.0.dev"

This reverts commit 79e0f19f2dcb35c957ac2d9ed69eca5b29af268f.

Reason for revert: Breaks tryjobs because pre-approvals didn't get applied across builders.

Original change's description:
> [infra] Update checked-in SDKs to 2.9.0-10.0.dev
> 
> Change-Id: I350c35cd11ab2365e0e2a844c13b92ebc1fa39c9
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149285
> Reviewed-by: William Hesse <whesse@google.com>

TBR=whesse@google.com,29642742b6693024c89de8232f2e2542cf7eedf7@google.com,askesc@google.com

Change-Id: Ia814e2d6cc7276293a5fca03b499377c37109647
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149324
Reviewed-by: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@google.com>
Commit-Queue: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk