VM: [Cleanup] Delete legacy code associated with BranchInstr.

runtime/vm/branch_optimizer.cc

Index: runtime/vm/branch_optimizer.cc
diff --git a/runtime/vm/branch_optimizer.cc b/runtime/vm/branch_optimizer.cc
index 62fdb47b041b6eafa0e1c1c5a2ef8f19969559c4..f68bbcaef3379903f93cec3ce13d18b07e604846 100644
--- a/runtime/vm/branch_optimizer.cc
+++ b/runtime/vm/branch_optimizer.cc
@@ -83,7 +83,6 @@ BranchInstr* BranchSimplifier::CloneBranch(Zone* zone,
   ComparisonInstr* new_comparison =
       comparison->CopyWithNewOperands(new_left, new_right);
   BranchInstr* new_branch = new (zone) BranchInstr(new_comparison);
-  new_branch->set_is_checked(branch->is_checked());
   return new_branch;
 }