Rewrite the varnish cookbook article

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | all
| Fixed tickets | #1505, #4176
yeah, you have a point here. okay, lets drop the whole pragma and HTTP 1.0 discussion.

so should we keep this tab but just put a comment in it that nothing needs to be done for varnish 4? or only have a varnish3 (and maybe 2) tab and explain in the text that for varnish4 nothing special needs to be done?