MDEV-26782 fixup: Remove dead code

trx_undo_reuse_cached(): Assert that this is being invoked on the
persistent rollback segment of the transaction, and remove dead code
that was handling cached temporary undo log. This was missed in
commit 51e62cb (MDEV-26782).

storage/innobase/trx/trx0undo.cc

@@ -1258,6 +1258,8 @@ trx_undo_reuse_cached(trx_t* trx, trx_rseg_t* rseg, trx_undo_t** pundo,
 {
 	ut_ad(rseg->is_persistent());
 	ut_ad(rseg->is_referenced());
+	ut_ad(rseg == trx->rsegs.m_redo.rseg);
+
 	if (rseg->needs_purge <= trx->id) {
 		/* trx_purge_truncate_history() compares
 		rseg->needs_purge <= head.trx_no
@@ -1293,10 +1295,6 @@ trx_undo_reuse_cached(trx_t* trx, trx_rseg_t* rseg, trx_undo_t** pundo,
 
 	trx_undo_mem_init_for_reuse(undo, trx->id, &trx->xid, offset);
 
-	if (rseg != trx->rsegs.m_redo.rseg) {
-		return block;
-	}
-
 	if (trx->dict_operation) {
 		undo->dict_operation = TRUE;
 		mtr->write<1,mtr_t::MAYBE_NOP>(*block,