wget: Reduce closure size

This reduces the wget closure from 377 MiB to 49 MiB, which is in
particular good for EC2 images, since they include wget. The main
changes:

* Disable libpsl - this isn't very big itself, but it pulls in libicu,
  which is 36 MiB. It also adds build-time dependencies on packages
  like gtk-doc, dblatex, tetex etc.

* Replace gnutls with openssl. The former pulls in runtime
  dependencies like guile, python, binutils, gcc, ncurses, etc.