Revert "Zero out auth structs before transfer"

This reverts commit ce8311c7e4.

The commit made test 2024 work but caused a regression with repeated
Digest authentication. We need to fix this differently.

lib/transfer.c

@@ -1433,10 +1433,6 @@ CURLcode Curl_pretransfer(struct SessionHandle *data)
 
   data->state.ssl_connect_retry = FALSE;
 
-  /* zero out auth state */
-  memset(&data->state.authhost, 0, sizeof(struct auth));
-  memset(&data->state.authproxy, 0, sizeof(struct auth));
-
   data->state.authproblem = FALSE;
   data->state.authhost.want = data->set.httpauth;
   data->state.authproxy.want = data->set.proxyauth;