Remove navigation.indexes from zensical features

Removes the left-side menu header in the Zensical-generated docs site.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: MariusStorhaug

.github/zensical.toml

@@ -11,7 +11,6 @@ favicon = "Assets/icon.png"
 features = [
     "navigation.instant",
     "navigation.instant.progress",
-    "navigation.indexes",
     "navigation.top",
     "navigation.tracking",
     "navigation.expand",