codegen : message.cc fix datetime type

src/codegen/gen_cpp_Message.ysl2

@@ -117,14 +117,8 @@ tstylesheet {
         param "type";
         param "name";
         param "classname" call "CamelCase" with "text", "../@name";
-        const "convert", "$type != 'timestamp'";
 
-        choose {
-            when "$convert"
-                > «concat('Java_foundation_pEp_jniadapter_', $classname, '__1', str:replace($name, '_', '_1'))»
-            otherwise
-                > «concat('Java_foundation_pEp_jniadapter_', $classname, '_', str:replace($name, '_', '_1'))»
-        }
+        > «concat('Java_foundation_pEp_jniadapter_', $classname, '__1', str:replace($name, '_', '_1'))»
     }
 
     template "*", mode=entry {