cleanup: remove comments field from ConstantRef

It is not used.

Bug: none
Test: m aidl_unittests
Change-Id: I726682a17d4f1d8ca04dc7d85abef3039c230f1b
diff --git a/aidl_const_expressions.cpp b/aidl_const_expressions.cpp
index ce236fe..3267cfc 100644
--- a/aidl_const_expressions.cpp
+++ b/aidl_const_expressions.cpp
@@ -733,9 +733,8 @@
   }
 }
 
-AidlConstantReference::AidlConstantReference(const AidlLocation& location, const std::string& value,
-                                             const std::string& comments)
-    : AidlConstantValue(location, Type::REF, value), comments_(comments) {
+AidlConstantReference::AidlConstantReference(const AidlLocation& location, const std::string& value)
+    : AidlConstantValue(location, Type::REF, value) {
   const auto pos = value.find_last_of('.');
   if (pos == string::npos) {
     field_name_ = value;