journald: don't enforce monotonicity of realtime clocks when copying entries

After all the point of the realtime clock (in contrast to the monotonic
clock) is that it does not have to be strictly monotonic, hence don't
enforce this when flushing the journal from /run to /var.

src/journal/journal-file.c

@@ -2312,9 +2312,6 @@ int journal_file_copy_entry(JournalFile *from, JournalFile *to, Object *o, uint6
             ts.monotonic < le64toh(to->header->tail_entry_monotonic))
                 return -EINVAL;
 
-        if (ts.realtime < le64toh(to->header->tail_entry_realtime))
-                return -EINVAL;
-
         n = journal_file_entry_n_items(o);
         items = alloca(sizeof(EntryItem) * n);