Applications+DevTools+MenuApplets: Drop "unix" pledge when possible

Now that the "unix" pledge is no longer required for socket I/O, we can
drop it after making the connections we need in a program.

In most GUI program cases, once we've connected to the WindowServer by
instantiating a GApplication, we no longer need "unix" :^)

Applications/SystemMonitor/main.cpp

@@ -56,7 +56,7 @@ int main(int argc, char** argv)
 
     GApplication app(argc, argv);
 
-    if (pledge("stdio proc shared_buffer rpath unix", nullptr) < 0) {
+    if (pledge("stdio proc shared_buffer rpath", nullptr) < 0) {
         perror("pledge");
         return 1;
     }