Cleanup: Security::ContextPtr removal, pt2

Cleanup: Security::ContextPtr removal, pt2

Make the ContextPointer for client TLS contexts extend out of
libsecurity up the stack of callers to their main place of
med/long-term storage.

This means the code outside location where SSL contexts are created
mostly no longer needs to worry about (non-)locking details. Just
about using a smart Pointer properly.

Since class SquidConfig is one of those places this involves linking
pinger with openssl libraries. That is likely a bug to fix later.