tidy appearance of cover page (#369)

index.qmd

@@ -1,5 +1,3 @@
-`r if (knitr::is_latex_output()) '<!--'`
-
 # Welcome {.unnumbered}
 
 This is the on-line version of work-in-progress **3rd edition** of "ggplot2: elegant graphics for data analysis" published by Springer.
@@ -10,5 +8,3 @@ It is not a [cookbook](https://r-graphics.org), and won't necessarily help you c
 But it will help you understand the details of the underlying theory, giving you the power to tailor any plot specifically to your needs.
 
 The book is written by [Hadley Wickham](http://hadley.nz), [Danielle Navarro](https://djnavarro.net), and [Thomas Lin Pedersen](https://www.data-imaginist.com).
-
-`r if (knitr::is_latex_output()) '-->'`