Primarily since we appear to compile require with C and not C++

This reverts commit 9b59288d.

Update CONFIG_SHELL

See merge request e3/e3-require!84

E3-752: Fetch dependencies recursively

See merge request e3/e3-require!83

* One test to catch invalid dependencies
* One test to catch architecture-dependent dependencies. Note that this itself does depend on
  the underlying architecture, which probably should be improved. But at the moment we only
  build for linux-based architectures, so this should be ok.