src: remove unused typedef

Seems to have been overlooked in commit dd93c53 ("Make node::DLOpen use
uv_dlopen") from 2011.

PR-URL: #11322
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Nikolai Vavilov <vvnicholas@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>

src/node.cc

@@ -2400,8 +2400,6 @@ struct node_module* get_linked_module(const char* name) {
   return mp;
 }
 
-typedef void (UV_DYNAMIC* extInit)(Local<Object> exports);
-
 // DLOpen is process.dlopen(module, filename).
 // Used to load 'module.node' dynamically shared objects.
 //