pc/wifi: do not execute driver on user stack

The 'with_libc' call at this point is not necessary and could be
harmful as it forces the usage of the user stack for the driver.
All code depending on this distinction should only be executed
from within the pthread.

Issue #4537.

repos/pc/src/drivers/wifi/pc/main.cc

@@ -110,8 +110,6 @@ struct Main
 	}
 };
 
-static Main *_main;
-
 
 /**
  * Return shared-memory message buffer
@@ -126,8 +124,5 @@ void *wifi_get_buffer(void)
 
 void Libc::Component::construct(Libc::Env &env)
 {
-	Libc::with_libc([&] () {
-		static Main server(env);
-		_main = &server;
-	});
+	static Main server(env);
 }