Only download a single tailwindcss binary

[cuihtlauac]

Only download a single tailwindcss binary

Bring back stuff removed when merging #2718

[tmattio]

I am not sure how adding a default alias tells dune to download a single binary?
The alias wasn't used anywhere, we're using the binary directly.

[cuihtlauac]

If default is not restricted to taildwindcss, it also contains the 4 platform specific binaries. Without this restriction, just doing make clean and make build downloads the 4 binaries.

Incidentally, having the binary copied to the local switch allowed it to survive dune clean

[tmattio]

That's a behaviour of Dune I didn't know about, thanks!