Maintenance: Remove dead Multicast Miss Stream feature (#1320)

Maintenance: Remove dead Multicast Miss Stream feature (#1320)

This feature was added in 1998 commit e66d792 for special "you are
absolutely certain you understand what you are doing" experiments and
considered "largely undocumented and unsupported" by its primary
author[^1]. The corresponding MULTICAST_MISS_STREAM code in
access_log.cc has not built since 2007 commit cc192b5 (at least):

* 'class Ip::Address' has no member named 's_addr'
* 'comm_open' was not declared in this scope
* 'comm_udp_sendto' was not declared in this scope
* 'mcastSetTtl' was not declared in this scope
* 'METHOD_GET' was not declared in this scope
* 'no_addr' was not declared in this scope
* no match for 'operator!=' (operand types are LogTags and LogTags_ot)

[^1]: Duane Wessels. 2004. Squid: The Definitive Guide. O'Reilly &
Associates, Inc., USA. See mcast_miss_addr documentation on page 390.