[vm/compiler] Partially revert "Replace LoadClassId for known cids."
[vm/compiler] Partially revert "Replace LoadClassId for known cids."

We still need to check for concrete types in
ConstantPropagator::VisitLoadClassId to avoid benchmark regressions.

Change-Id: Ie3a7e3aaa3b261c34760308f3cb1d328ce2d8493
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103520
Commit-Queue: Teagan Strickland <cce218d042444252b7ac446d60910fca7732559c@google.com>
Reviewed-by: Martin Kustermann <a35dd5b79fac84b2bb3b026a16b8becc55af5961@google.com>

dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk