Fix a memory leak in the afalg engine

The AFALG engine created a global EVP_CIPHER instance but was not freeing
it up when the engine was destroyed.
Reviewed-by: NRich Salz <rsalz@openssl.org>

engines/afalg/e_afalg.c

@@ -844,6 +844,8 @@ static int afalg_finish(ENGINE *e)
 static int afalg_destroy(ENGINE *e)
 {
     ERR_unload_AFALG_strings();
+    EVP_CIPHER_meth_free(_hidden_aes_128_cbc);
+    _hidden_aes_128_cbc = NULL;
     return 1;
 }