Removed tcp-banger* and pconn-banger tools (#1236)

Removed tcp-banger* and pconn-banger tools (#1236)

We do not have enough resources/demand for maintaining these tools, they
do require maintenance, and there are better tools available.

* tcp-banger2 is not built by default and probably could not be built at
  all since at least 2006 commit 5679212.

* tcp-banger3 lacked build rules since inception (1998 commit 2742510)
  and probably could not be built manually (by mimicking tcp-banger2
  build commands) without warnings since 2002 commit 88d8a2a.

* pconn-banger lacked build rules since inception (1997 commit eb5f55b)
  and probably could not be built manually since at least 2007 commit
  cc192b5.

* tcp-banger.pl has portability and code quality issues; its basic
  functionality is supported by squidclient, wget, curl, and others.

Co-authored-by: Alex Rousskov <rousskov@measurement-factory.com>