aconfig: update cpp codegen to use static methods

Update c++ codegen to static methods interface.

Bug: b/279483801
Test: atest aconfig.test
Change-Id: I78da3bbca6240bee660c692807930d00f2242b0a
diff --git a/tools/aconfig/templates/cpp.template b/tools/aconfig/templates/cpp.template
index 93f9b80..aa36d94 100644
--- a/tools/aconfig/templates/cpp.template
+++ b/tools/aconfig/templates/cpp.template
@@ -6,18 +6,15 @@
 {{ endif }}
 namespace {cpp_namespace} \{
     {{ for item in class_elements}}
-    class {item.flag_name} \{
-        public:
-            virtual const bool value() \{
-                {{ if item.readwrite- }}
-                return GetServerConfigurableFlag(
-                    "{item.device_config_namespace}",
-                    "{item.device_config_flag}",
-                    "{item.default_value}") == "true";
-                {{ -else- }}
-                return {item.default_value};
-                {{ -endif }}
-            }
+    static const bool {item.flag_name}() \{
+        {{ if item.readwrite- }}
+        return GetServerConfigurableFlag(
+            "{item.device_config_namespace}",
+            "{item.device_config_flag}",
+            "{item.default_value}") == "true";
+        {{ -else- }}
+            return {item.default_value};
+        {{ -endif }}
     }
     {{ endfor }}
 }