Cleanup the Javascript and CSS of our custom TOC

Author: Urgau

src/doc/rustc/theme/pagetoc.css

@@ -10,14 +10,6 @@
     min-width: 50px;
 }
 
-.previous {
-    /*
-    adjust the space between the left sidebar or the left side of the screen 
-    and the button that leads to the previous page
-    */
-    margin-left: var(--page-padding);
-}
-
 @media only screen {
     @media (max-width: 1179px) {
         .sidebar-hidden #sidetoc {

src/doc/rustc/theme/pagetoc.js

@@ -71,7 +71,8 @@ function updatePageToc(elem = undefined) {
     }
 }
 
-if (document.getElementById("sidetoc") === null) {
+if (document.getElementById("sidetoc") === null &&
+    document.getElementsByClassName("header").length > 0) {
     // The sidetoc element doesn't exist yet, let's create it
 
     // Create the empty sidetoc and pagetoc elements
@@ -80,16 +81,11 @@ if (document.getElementById("sidetoc") === null) {
     sidetoc.id = "sidetoc";
     pagetoc.id = "pagetoc";
     sidetoc.appendChild(pagetoc);
-    
+
     // And append them to the current DOM
     const main = document.querySelector('main');
     main.insertBefore(sidetoc, main.firstChild);
-}
 
-if (document.getElementsByClassName("header").length <= 1) {
-    // There's one or less headings, we don't need a page table of contents
-    document.getElementById("sidetoc").remove();
-} else {
     // Populate sidebar on load
     window.addEventListener("load", () => {
         for (const header of document.getElementsByClassName("header")) {