n-api: remove unused napi_env member

`wrap_template` is no longer used since we've switched to v8::Private.

PR-URL: #21127
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

Author: Gabriel Schulhof

src/node_api.cc

@@ -23,7 +23,6 @@ struct napi_env__ {
         loop(_loop) {}
   v8::Isolate* isolate;
   node::Persistent<v8::Value> last_exception;
-  node::Persistent<v8::ObjectTemplate> wrap_template;
   node::Persistent<v8::ObjectTemplate> function_data_template;
   node::Persistent<v8::ObjectTemplate> accessor_data_template;
   napi_extended_error_info last_error;