Revert "VM: Handle null-comparisons in the flow graph type propagation"

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index a0fb25eb0f43d1baa35afd57d1625da01b6cd93d..766a6836e4fad3bcfc72638c9fb21a20d0ab2c93 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -104,7 +104,11 @@ class CompileType : public ZoneAllocated {
   static CompileType Create(intptr_t cid, const AbstractType& type);
 
   CompileType CopyNonNullable() const {
-    return CompileType(kNonNullable, kIllegalCid, type_);
+    return CompileType(kNonNullable, cid_, type_);
+  }
+
+  static CompileType CreateNullable(bool is_nullable, intptr_t cid) {
+    return CompileType(is_nullable, cid, NULL);
   }
 
   // Create a new CompileType representing given abstract type. By default