Fix repo link; remove old gitbook renderer

Fixes #1015

_output.yaml

@@ -1,24 +1,12 @@
 bookdown::bs4_book:
   theme:
     primary: "#637238"
-  repo: https://github.com/hadley/r4ds
+  repo:
+    base: https://github.com/hadley/r4ds
+    branch: main
   includes:
     in_header: [ga_script.html]
 
-bookdown::gitbook:
-  includes:
-    in_header: [ga_script.html]
-  config:
-    toc:
-      collapse: section
-      before: |
-        <li><strong><a href="./">R for Data Science</a></strong></li>
-    edit:
-      link: https://github.com/hadley/r4ds/edit/main/%s
-      text: "Edit"
-    sharing: no
-  css: r4ds.css
-
 bookdown::pdf_book:
   latex_engine: "xelatex"