CLEANUP: Fix wrong, outdated, and irrelevant comments

CLEANUP: Fix wrong, outdated, and irrelevant comments

- Remove leftover debug printf() calls in masking.c (one with
  typo /n instead of \n)
- Remove commented-out code: FLAGS_SJOIN, FLAGS_SNICK, UMODE_WEBTV,
  hidden[] struct fields, aJinxItem, old initconf(), pv[4] declarations,
  debuglevel block in ircd.c, fixme/commented code in s_serv.c
- Remove unused #define debug 1 in s_conf.c
- Fix outdated comments: TSpre7 reference in s_numeric.c, DreamForge
  reference in s_ping.c, "KLUDGE to get it work" in s_bsd.c,
  "This used to be the case. Now it no longer is." in s_bsd.c,
  "Impact? Let's see..." in list.c, "Yuck. Stuck." in packet.c
- Replace misleading comments with accurate descriptions
- Add clarifying comments: hash table compare macro, IRC numeric
  parsing, fd remapping on close, server DNS verification

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>