Make target `serve_local` is broken because of missing `build_loadable_unsigned`

### What happens?

Make target `serve_local` depends on `build_loadable_unsigned` which is now missing, so this make target cannot be run.

I was looking for something like this because I was trying to run duckdb-wasm with extension signing off, as this is needed to test locally built extensions. (see also https://github.com/isaacbrodsky/h3-duckdb/issues/71)

### To Reproduce

`make serve_local`

### Browser/Environment:

NA

### Device:

NA

### DuckDB-Wasm Version:

main

### DuckDB-Wasm Deployment:

NA

### Full Name:

NA

### Affiliation:

NA