nixosTests.agda.base: fix build

the binary adga-mode has been deprecated
one is supposed to use the main binary with --emacs-mode instead

Author: quantenzitrone

nixos/tests/agda/base.nix

@@ -26,7 +26,6 @@ in
   testScript = ''
     # agda and agda-mode are in path
     machine.succeed("agda --version")
-    machine.succeed("agda-mode")
 
     # Minimal script that typechecks
     machine.succeed("touch TestEmpty.agda")