Clean up config.toml.

- Hugo 0.28 and newer use Chroma, a Go syntax highlight library:

  https://gohugo.io/content-management/syntax-highlighting/

  Setting the site configuration variable `pygmentsUseClassic` to true
  reverts to Pygments highlighting, allowing learntla.com to continue
  to use https://github.com/hwayne/tla-pygments.

- Remove the menu parameter, per
  4101699

- Use hugo-theme-learn's disableSearch and
  disableInlineCopyToClipBoard to disable features previously disabled
  by overriding footer.html.

config.toml

@@ -3,8 +3,10 @@ baseurl = "http://learntla.com"
 title = "Learn TLA"
 theme = "hugo-theme-learn"
 googleAnalytics = "UA-90708265-1"
+pygmentsUseClassic = true
 PygmentsCodeFences = true
 
 [Params]
   Author = "Hillel Wayne"
-  menu = ["introduction", "pluscal", "tla", "models", "concurrency", "temporal-logic", "techniques", "reference"]
+  disableSearch = true
+  disableInlineCopyToClipBoard = true