libstore: Remove lockCPU dead code

Left over from 9747ea84b, https://github.com/NixOS/nix/pull/5821

perl/lib/Nix/Store.xs

@@ -27,7 +27,6 @@ static ref<Store> store()
     if (!_store) {
         try {
             initLibStore();
-            settings.lockCPU = false;
             _store = openStore();
         } catch (Error & e) {
             croak("%s", e.what());

src/libstore/globals.cc

@@ -49,7 +49,6 @@ Settings::Settings()
     , nixDaemonSocketFile(canonPath(getEnvNonEmpty("NIX_DAEMON_SOCKET_PATH").value_or(nixStateDir + DEFAULT_SOCKET_PATH)))
 {
     buildUsersGroup = getuid() == 0 ? "nixbld" : "";
-    lockCPU = getEnv("NIX_AFFINITY_HACK") == "1";
     allowSymlinkedStore = getEnv("NIX_IGNORE_SYMLINK_STORE") == "1";
 
     auto sslOverride = getEnv("NIX_SSL_CERT_FILE").value_or(getEnv("SSL_CERT_FILE").value_or(""));