statistics-channels /xml/v2 is removed but still documented

Summary

ARM contains documentation of statistics-channels format of /xml/v2. But code does not allow such format anymore. Only /xml/v3 and /json/v1 are supported in code.

BIND version used

BIND 9.11.4-RedHat-9.11.4-2.fc27 It seems present also in devel version

Steps to reproduce

grep '/v2' -r doc doc/arm/Bv9ARM.ch05.html: http://127.0.0.1:8888/xml/v2 for version 2 doc/arm/Bv9ARM-book.xml: http://127.0.0.1:8888/xml/v2 for version 2

(How one can reproduce the issue - this is very important.)

What is the current bug behavior?

Documents statistics format that cannot be configured.

What is the expected correct behavior?

Do not mention format that is not available.

Possible fixes

(If you can, link to the line of code that might be responsible for the problem.)