This method mimicks std::unique_ptr::reset(), but adds an obscure
"add_ref" parameter which is error prone. Since nobody uses this
method, and this method is all about dealing with raw pointers which
we shouldn't be doing, let's remove it.
* origin/topic/neverlord/intrusive-ptr:
Add API documentation to IntrusivePtr
Rename make{ Counted => _intrusive }
Remove braces around single return statements
Integrate review feedback
Add and use new IntrusivePt type in Zeek
Manual memory management via Ref/Unref is verbose and prone to error. An
intrusive smart pointer automates the reference counting, makes code
more robust (in particular w.r.t. to exceptions) and reduces boilerplate
code. A big benefit of the intrusive smart pointers for Zeek is that
they can co-exist with the manual memory management. Rather than having
to port the entire code base at once, we can migrate components
one-by-one. In this first step, we add the new template
`IntrusivePtr<T>` and start using it in the Broker Manager. This makes
the previous `unref_guard` obsolete.
