Remove squidclient (#1514)

Remove squidclient (#1514)

Since recent commit a4e35bd removed cache_object support, popular
clients like wget and curl can do everything squidclient can, with one
exception: They cannot expand `mgr:foo` macros into
`http://localhost:3128/squid-internal-mgr/foo` URLs. That single feature
is easily emulated and not worth keeping (fairly heavy) squidclient for,
especially since recent Squid security improvements often require
customizing squidclient commands with more and more options (to address
problems tracked in Squid bug 5283).