tests/functional2/lang: Migrate autoargs

autoargs get their own folder and are not allowed with the other
function args tests, just like they deserve their own ring of hell

It shall be noted though that this test is particularly pointless, as it
merely tests the normal argument passing (which is fine), and not the
✨magic✨ autoargs actually provide

Change-Id: Ia2dc00754a13c02e4926200141f90bc797820a15

tests/functional/lang/eval-okay-autoargs.flags

@@ -1 +0,0 @@
---arg lib import(./lib.nix) --argstr xyzzy xyzzy! -A result

tests/functional2/lang/function-autoargs/test.toml

@@ -0,0 +1,3 @@
+[[test]]
+runner = "eval-okay"
+flags = [ "--arg", "lib", "import(./lib.nix)", "--argstr", "xyzzy", "xyzzy!", "-A", "result" ]