Revert "single-pool: Allow stake config to be anything in tests (#6543)" (#6544)

This reverts commit b32ab74.

Author: joncinque

single-pool/program/tests/accounts.rs

@@ -157,12 +157,6 @@ async fn fail_account_checks(test_mode: TestMode) {
         if instruction_account.pubkey == accounts.alice.pubkey() {
             continue;
         }
-        // stake config address can also be arbitrary. Remove all usage of
-        // `stake::config` with the upgrade to 2.0
-        #[allow(deprecated)]
-        if instruction_account.pubkey == stake::config::id() {
-            continue;
-        }
 
         let prev_pubkey = instruction_account.pubkey;
         instruction_account.pubkey = Pubkey::new_unique();