Check wkhtmltopdf dependency for help.pdf build

[qarkai]

Note: wkhtmltopdf is archived and no longer maintained.

[caclark]

This was a very bad idea to use wkhtmltopdf (although it seemed quick-and-easy-and-no-thinking at the time - and the implementation was bad).

I am going to revert that commit.

Deriving the pdf from the xml is a better way.

[qarkai]

Close then.