[dart2js] Make some operator == use just identical.

b/384749454 demonstrates that defining `operator ==` to agree with
`hashCode` can cause some problematic semantic differences. Although we
haven't seen issues coming from these classes, this removes the new
semantics for `HBasicBlock` and `ValueSetNode`.

Change-Id: Ieb46f3ea2ab136cf990b6d8ec38f62977eddf547
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/401386
Commit-Queue: Nate Biggs <[email protected]>
Auto-Submit: Mayank Patke <[email protected]>
Reviewed-by: Nate Biggs <[email protected]>

Author: fishythefish

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

@@ -826,8 +826,7 @@ class HBasicBlock extends HInstructionList {
   int get hashCode => id;
 
   @override
-  bool operator ==(other) =>
-      identical(this, other) || other is HBasicBlock && id == other.id;
+  bool operator ==(other) => identical(this, other);
 
   bool get isNew => _status == _BasicBlockStatus.new_;
   bool get isOpen => _status == _BasicBlockStatus.open;

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

@@ -169,6 +169,5 @@ class ValueSetNode {
   ValueSetNode(this.value, this.hash, this.next);
 
   @override
-  bool operator ==(other) =>
-      identical(this, other) || other is ValueSetNode && hash == other.hash;
+  bool operator ==(other) => identical(this, other);
 }