Missing attribute documentation for Tracks

The old documentation included a section on attributetype [Track](https://asacolips.gitbook.io/pbta-system/configuration-reference-1/attribute-types#track). The [new documentation](https://github.com/asacolips-projects/pbta/wiki/Attribute-Types) does not. They still exist in the code,if they should not be used maybe there should be a note that they are deprecated.