fix: Remove unsupported book.toml keys

Removed configuration keys from book.toml not supported by the current
version of mdbook, which were causing build warnings.

book.toml

@@ -1,8 +1,7 @@
 [book]
+title = "The Bin"
 authors = ["Matthew Binning"]
 language = "en"
-multilingual = false
-title = "The Bin"
 
 [build]
 build-dir = "blog"
@@ -13,8 +12,8 @@ smart-punctuation = true
 git-repository-url = "https://forgejo.binning.net/matthew.binning/www"
 edit-url-template = "https://forgejo.binning.net/matthew.binning/www/src/branch/main/{path}"
 additional-css = ["theme/sepia.css"]
+additional-js = ["theme/navbar.js"]
 no-section-label = true
-copy-fonts = false
 fold.enable = true
 fold.level = 0