[dart2js] Simplify HTypeKnow.isRedundant

After 0bb3adb it seems we should not
need the HTypeKnown to stick around since the knownType can no longer
change.

Bug: #60327
Change-Id: I575816a11e41e75acebecde1c32d37d251b5947b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/426343
Reviewed-by: Mayank Patke <[email protected]>
Commit-Queue: Stephen Adams <[email protected]>

Author: rakudrama

pkg/compiler/lib/src/ssa/nodes.dart

@@ -4088,9 +4088,6 @@ class HTypeKnown extends HCheck {
 
   bool isRedundant(JClosedWorld closedWorld) {
     AbstractValueDomain abstractValueDomain = closedWorld.abstractValueDomain;
-    if (abstractValueDomain.containsAll(knownType).isPotentiallyTrue) {
-      return false;
-    }
     AbstractValue inputType = checkedInput.instructionType;
     return abstractValueDomain.isIn(inputType, knownType).isDefinitelyTrue;
   }