Rm preview js

assets/js/dark-mode-preview.js

-document.addEventListener("DOMContentLoaded", function () {
-  const toggleDarkMode = document.querySelector(".js-toggle-dark-mode")
-  const cssFile = document.querySelector('[rel="stylesheet"]')
-  const originalCssRef = cssFile.getAttribute("href")
-  const darkModeCssRef = originalCssRef.replace(
-    "just-the-docs.css",
-    "dark-mode-preview.css"
-  )
-  const buttonCopy = ["Return to the light side", "Preview dark color scheme"]
-  const updateButtonText = function (toggleDarkMode) {
-    toggleDarkMode.textContent === buttonCopy[0]
-      ? (toggleDarkMode.textContent = buttonCopy[1])
-      : (toggleDarkMode.textContent = buttonCopy[0])
-  }
-
-  jtd.addEvent(toggleDarkMode, "click", function () {
-    if (cssFile.getAttribute("href") === originalCssRef) {
-      cssFile.setAttribute("href", darkModeCssRef)
-      updateButtonText(toggleDarkMode)
-    } else {
-      cssFile.setAttribute("href", originalCssRef)
-      updateButtonText(toggleDarkMode)
-    }
-  })
-})