nvim, aerc: Update templates and use threading respectively

.config/aerc/aerc.conf

@@ -260,7 +260,7 @@ styleset-name=dracula
 # (IMAP server or notmuch), threads will be built by the client.
 #
 # Default: false
-#threading-enabled=false
+threading-enabled=false
 
 # Force client-side thread building
 #

.config/nvim/templates/skeleton.cpp

@@ -1,7 +0,0 @@
-/* Copyright 2023 all wrongs deserved */
-#include <iostream>
-
-int main() {
-
-    return 0;
-}