Get rid of srvx-broadcast announcements. (They do not scale.)

Get rid of srvx-broadcast announcements.  (They do not scale.)

src/global.h (MESSAGE_RECIPIENT_ANNOUNCE): Remove.

src/global.c (KEY_ANNOUNCEMENTS_DEFAULT): Remove.
  (global_conf): Remove announcements_default field.
  (message_create): Do not recognize "announce[ment]" target.
  (messageType): Remove MESSAGE_RECIPIENT_ANNOUNCE condition.
  (message_send): Remove MESSAGE_RECIPIENT_ANNOUNCE condition.
  (cmd_notice): Do not recognize "announce[ment]" target.
  (global_conf_read): Do not look up announcements_default key.

src/global.help (TARGET): Remove ANNOUNCEMENT target.

src/nickserv.h (struct handle_info): Remove announcements field.

src/nickserv.c (KEY_ANNOUNCEMENTS): Remove.
  ("NSMSG_INVALID_ANNOUNCE"): Remove.
  ("NSMSG_SET_ANNOUNCEMENTS"): Remove.
  (register_handle): Do not assign to hi->announcements.
  (set_list): Remove ANNOUNCEMENTS from the default list.
  (opt_announcements): Remove.
  (nickserv_saxdb_write): Remove announcements code.
  (nickserv_db_read_handle): Remove announcements code.
  (init_nickserv): Do not register opt_announcements function.

nickserv.help (SET): Remove ANNOUNCEMENTS option.