fuzz-journal-remote: write to /dev/null not stdout

This makes the fuzzing much more efficient.
The case from 056129d is still detected properly.

src/fuzz/fuzz-journal-remote.c

@@ -13,6 +13,7 @@
 #include "strv.h"
 
 int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
+        _cleanup_fclose_ FILE *dev_null = NULL;
         RemoteServer s = {};
         char name[] = "/tmp/fuzz-journal-remote.XXXXXX.journal";
         void *mem;
@@ -47,8 +48,10 @@ int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) {
         r = sd_journal_open_files(&j, (const char**) STRV_MAKE(name), 0);
         assert_se(r >= 0);
 
+        assert_se(dev_null = fopen("/dev/null", "w"));
+
         for (mode = 0; mode < _OUTPUT_MODE_MAX; mode++) {
-                r = show_journal(stdout, j, mode, 0, 0, -1, 0, NULL);
+                r = show_journal(dev_null, j, mode, 0, 0, -1, 0, NULL);
                 assert_se(r >= 0);
 
                 r = sd_journal_seek_head(j);