free: instead of Curl_safefree()

Since we just started make use of free(NULL) in order to simplify code,
this change takes it a step further and:

- converts lots of Curl_safefree() calls to good old free()
- makes Curl_safefree() not check the pointer before free()

The (new) rule of thumb is: if you really want a function call that
frees a pointer and then assigns it to NULL, then use Curl_safefree().
But we will prefer just using free() from now on.

lib/http_proxy.c

@@ -212,7 +212,7 @@ CURLcode Curl_proxyCONNECT(struct connectdata *conn,
           failf(data, "Failed sending CONNECT to proxy");
       }
 
-      Curl_safefree(req_buffer);
+      free(req_buffer);
       if(result)
         return result;
 
@@ -463,7 +463,7 @@ CURLcode Curl_proxyCONNECT(struct connectdata *conn,
 
                     result = Curl_http_input_auth(conn, proxy, auth);
 
-                    Curl_safefree(auth);
+                    free(auth);
 
                     if(result)
                       return result;