Forget non-peer access details (#1378)

Forget non-peer access details (#1378)

We were using the CachePeer class to record the address of each non-peer
sending us certain unwanted ICP responses, along with the number of such
responses and a histogram of associated ICP opcodes. Since 1997 commit
e102ebd, these historical records were accumulated without a limit and
linearly searched, endangering a Squid instance that used ICP. Using
CachePeer to store this non-cache_peer information also complicated
cache_peer code.

This change removes these records and the corresponding mgr:non_peers
report, leaving just the cache.log warning about unexpected messages.
The warning is useful because these ICP messages from non-peers indicate
a cache hierarchy misconfiguration or a fairly sophisticated attack.

This is the simplest fix that minimizes Squid and developer resources
spent on handling these errors.