Cleanup: un-wrap C++ header includes

Cleanup: un-wrap C++ header includes

Coding guideline is now that standard C++ headers are not to be
wrapped in HAVE_ macros.

* Remove HAVE_ macros for currently wrapped C++ headers.
  Includes removing autoconf checks.

* Replace C includes with C++ includes where possible

Also, <cstdio> / <stdio.h> has issues on 64-bit systems and a
portable fixed version is provided by libcompat via squid.h
It should not be included anywhere in the Squid sources.