Revert "functional2: fix in the development shell"

This reverts commit 42691f0d94.

Reason for revert: darwin builds time out now, apparently due to newly appearing infinite loops in the test suite

Change-Id: I81a09efd53636a287f3095ac87ed8854b6e57922

tests/functional2/testlib/global_assets/config.nix.template

@@ -17,7 +17,7 @@ rec {
   mkDerivation = args:
     derivation ({
       inherit system;
-      builder = "@shell@";
+      builder = "/bin/sh";
       args = ["-e" args.builder or (builtins.toFile "builder-${args.name}.sh" ''
         if [ -e "$NIX_ATTRS_SH_FILE" ]; then source $NIX_ATTRS_SH_FILE; fi;
         eval "$buildCommand"

tests/functional2/testlib/utils.py

@@ -144,7 +144,6 @@ def get_global_asset(name: str) -> Fileish:
                 "system": os.environ.get("system"),  # noqa: SIM112 # system is actually lowercase here
                 # Either just the build shell or entire global path if we are darwin
                 "path": os.environ.get("BUILD_TEST_SHELL") or os.environ.get("PATH"),
-                "shell": Path(os.environ.get("BUILD_TEST_SHELL") or "/bin") / "sh",
             },
         )
     return CopyFile(functional2_base_folder / "testlib" / "global_assets" / name)