v3.0.0: Drop support for D1, rename production to prod

This release comes with two breaking changes:

• First, all D1 support and mentions have been removed,
  as no project is known to still use D1.

• Second, for consistency, the production flavor has been
  renamed to prod, so it better mirrors dev.
  Those wishing to still use production can add it to VALID_FLAVORS,
  however the defaults that come with prod will not be applied.