Upstream now provides a library file for the builtin library and ensured
that the existing interface files will be used regardless of whether
--local-interfaces is in effect. Hence, Agda will not try to write to
the Nix store anymore except if the build flags are changed.
The one-line test is hard to fix in a readable manner
and doesn't really add value above the hello-world test.
So rather simplify to reduce maintenance.
The Everthing module is not part of a library and should therefore
not be copied to the nix store.
This is particularly bad, if the Everything module is defined in
an agda library included directory, e.g. consider an agda-lib with
include: .
and Everything.agda in the project root (.), in which case the
Everything module would become part of the library.
If multiple such projects are in the dependency tree, the Everything
module becomes ambiguous and the build would fail.
