arg : clean up handling --mmproj with -hf (#13082)

* arg : clean up handling --mmproj with -hf

* rm change about no_mmproj

* Revert "rm change about no_mmproj"

This reverts commit 2cac8e0efb629d66c612f137e75d562f94bb9e6c.

* handle no_mmproj explicitly

* skip download mmproj on examples not using it

examples/llava/mtmd-cli.cpp

@@ -261,6 +261,7 @@ int main(int argc, char ** argv) {
 
     if (params.mmproj.path.empty()) {
         show_additional_info(argc, argv);
+        LOG_ERR("ERR: Missing --mmproj argument\n");
         return 1;
     }