entry_dedupe should not copy reserved tags

[lemon24]

On my database from 2025-11-17, .readtime was copied on a bunch of duplicates:

sqlite> select count(key) as c, key from entry_tags group by key order by c desc;
22220|.readtime
23|.duplicate.1.of..readtime
2|.comments
1|.comment
1|.duplicate.2.of..readtime
1|tweeted

This doesn't hurt, but it's not particularly useful either (and it clutters stuff for no reason).

Of note, .comment(s) are not reserved, I just kinda misappropriated the reserved tag notation. I think that for now it may be fine to skip all reserved tags, but if a plugin were to implement a comment system using reserved tags, we'd need a way to tell entry_dedupe to copy them.