Get rid of "list of all configuration variables"

[rdb]

A reference of all variables has no place in a manual. Instead, such a list should be automatically generated as part of the Reference (see #21).

We could have a list of variables under each module generated by the API reference generator. Then, we can create cross-references to the documentation for each particular variable from the manual text where this variable is mentioned.

[Moguri]

I am fine with not having the page in the manual proper, but I do reference this page a lot, so some form of replacement would be appreciated.

[rdb]

Yes, I think it should be automatically generated in the reference section. I don't intend to remove it before we have a replacement.