squid: update to 7.1

squid: update to 7.1

- Use GitHub for sources URL
- Remove autoreconf fixup (it works out-of-the-box)
- Remove squid-mod-cachemgr package since cachemgr.cgi was removed upstream
- Rename ac_cv_epoll_works to squid_cv_epoll_works to follow upstream
- Don't customize target CFLAGS and LDFLAGS (they work as is)
- Remove nettle configure patch - upstream handles it correctly now
- Remove dummy comment in config menu

Signed-off-by: Aleksey Vasilenko <redacted>