WindowServer+LibVT: Convert some dbgprintf() to dbg()

These kept annoying me, because these were the only two lines in the default
boot log that went unattributed.

Services/WindowServer/main.cpp

@@ -111,7 +111,7 @@ int main(int, char**)
         return 1;
     }
 
-    dbgprintf("Entering WindowServer main loop.\n");
+    dbg() << "Entering WindowServer main loop";
     loop.exec();
     ASSERT_NOT_REACHED();
 }