website: remove unused root path on building website (#3248)

We no longer use the `--root` option of `build_website.py` since we have
moved to jqlang.org (from jqlang.github.io/jq where the root was `/jq`).
We don't need the option on local development either since `http.server`
has the `-d` option to specify the directory to serve from.

docs/templates/index.html.j2

@@ -8,7 +8,7 @@
     <main id="main" class="container-lg">
       <div class="row">
         <div class="col-md-6 text-center p-3">
-          <h1><img src="{{ root }}/jq.svg" class="img-fluid" alt="jq" width="400" height="220"></h1>
+          <h1><img src="/jq.svg" class="img-fluid" alt="jq" width="400" height="220"></h1>
         </div>
         <div class="col-md-6 d-flex flex-column justify-content-center text-center align-items-center">
           <h2 class="px-1" style="width:16em">{{ blurb }}</h2>
@@ -23,7 +23,7 @@
               <li><a class="dropdown-item" href="https://github.com/jqlang/jq/releases/download/jq-1.7.1/jq-macos-amd64" aria-label="Link to download executable: macOS (AMD64)"><span class="bi bi-download me-2" aria-hidden="true"></span>macOS (AMD64)</a></li>
               <li><a class="dropdown-item" href="https://github.com/jqlang/jq/releases/download/jq-1.7.1/jq-macos-arm64" aria-label="Link to download executable: macOS (ARM64)"><span class="bi bi-download me-2" aria-hidden="true"></span>macOS (ARM64)</a></li>
               <li><a class="dropdown-item" href="https://github.com/jqlang/jq/releases/download/jq-1.7.1/jq-windows-amd64.exe" aria-label="Link to download executable: Windows (AMD64)"><span class="bi bi-download me-2" aria-hidden="true"></span>Windows (AMD64)</a></li>
-              <li><a class="dropdown-item" href="{{ root }}/download/">Other platforms, older versions, and source</a></li>
+              <li><a class="dropdown-item" href="/download/">Other platforms, older versions, and source</a></li>
             </ul>
             <a class="btn btn-primary text-nowrap" href="https://jqplay.org" target="_blank" rel="noopener">
               Try online at jqplay.org!<span class="bi bi-box-arrow-up-right ms-1" aria-hidden="true"></span>