fetchPnpmDeps,pnpmConfigHook: drop pnpmWorkspace migration guards

The deprecated singular `pnpmWorkspace` attribute (superseded by
`pnpmWorkspaces` in #350751) has no remaining in-tree users, so the
assert and hook check pointing users to the new attribute are no
longer needed.

Assisted-by: Claude Code (Claude Opus 4.7)

pkgs/build-support/node/fetch-pnpm-deps/default.nix

@@ -59,11 +59,6 @@ in
         else
           pnpm-fixup-state-db;
     in
-    # pnpmWorkspace was deprecated, so throw if it's used.
-    assert
-      !args ? pnpmWorkspace
-      || throw "fetchPnpmDeps: `pnpmWorkspace` is no longer supported, please migrate to `pnpmWorkspaces`.";
-
     assert
       fetcherVersion != null
       || throw "fetchPnpmDeps: `fetcherVersion` is not set, see https://nixos.org/manual/nixpkgs/stable/#javascript-pnpm-fetcherVersion.";

pkgs/build-support/node/fetch-pnpm-deps/pnpm-config-hook.sh

@@ -74,11 +74,6 @@ pnpmConfigHook() {
     # See: https://pnpm.io/settings#packageimportmethod
     pnpm config set package-import-method clone-or-copy
 
-    if [[ -n "$pnpmWorkspace" ]]; then
-        echo "'pnpmWorkspace' is deprecated, please migrate to 'pnpmWorkspaces'."
-        exit 2
-    fi
-
     echo "Installing dependencies"
     if [[ -n "$pnpmWorkspaces" ]]; then
         local IFS=" "