hsts: Remove pointless call to free in errorpath

The line variable will always be NULL in the error path, so remove
the free call since it's pointless.

Closes #6170
Reviewed-by: Daniel Stenberg <daniel@haxx.se>

lib/hsts.c

@@ -498,7 +498,6 @@ static CURLcode hsts_load(struct hsts *h, const char *file)
 
   fail:
   Curl_safefree(h->filename);
-  free(line);
   fclose(fp);
   return CURLE_OUT_OF_MEMORY;
 }