Revert "[VM/runtime] Fix type tests with LHS FutureOr (fixes #38906)."

This reverts commit 3ef5270f7173fc5cc6698051ff4d5f23fe186780.

Reason for revert: precomp not tested by CQ and failing

Original change's description:
> [VM/runtime] Fix type tests with LHS FutureOr (fixes #38906).
> 
> Fixes tests/language_2/subtyping_static/future_or_subtype_test
> Also simplifies code making use of TypeAtNullSafe().
> 
> Change-Id: I045a030b2ece9d6980f7a9ba785948f0c10f697b
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/135625
> Commit-Queue: Régis Crelier <regis@google.com>
> Reviewed-by: Alexander Markov <alexmarkov@google.com>

TBR=alexmarkov@google.com,asiva@google.com,regis@google.com,liama@google.com

Change-Id: Ie6399e6c6cfd602dc7388a1a9ef5a7c335e70c65
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136528
Reviewed-by: Régis Crelier <regis@google.com>
Commit-Queue: Régis Crelier <regis@google.com>