[x/blog] template: remove search box

The custom search algorithm that was previously implemented and served
on the golang.org website has been removed via CL 292590 and CL 293412,
so remove the search box in the blog.golang.org header too.

For golang/go#44357.
Fixes golang/go#44912.

Change-Id: I51478ccb568e94df50d0dc6920a26c8f30a04c3c
Reviewed-on: https://go-review.googlesource.com/c/blog/+/311969
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
X-Blog-Commit: 5d47918ba6b83a86f5752483a2310cda931dd255

blog/template/root.tmpl

@@ -103,23 +103,6 @@
         <li class="Header-menuItem"><a href="{{.GodocURL}}/help/">Help</a></li>
         <li class="Header-menuItem"><a href="{{.BasePath}}/">Blog</a></li>
         <li class="Header-menuItem"><a href="https://play.golang.org/">Play</a></li>
-        <li class="Header-menuItem Header-menuItem--search">
-          <form class="HeaderSearch" role="search" action="{{.GodocURL}}/search">
-            <input class="HeaderSearch-input"
-                  type="search"
-                  name="q"
-                  placeholder="Search"
-                  aria-label="Search"
-                  autocapitalize="off"
-                  autocomplete="off"
-                  autocorrect="off"
-                  spellcheck="false"
-                  required>
-            <button class="HeaderSearch-submit" aria-label="Search">
-              <!-- magnifying glass: --><svg class="HeaderSearch-icon" width="24" height="24" viewBox="0 0 24 24"><title>Search</title><path d="M15.5 14h-.79l-.28-.27C15.41 12.59 16 11.11 16 9.5 16 5.91 13.09 3 9.5 3S3 5.91 3 9.5 5.91 16 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l5 4.99L20.49 19l-4.99-5zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z"/><path d="M0 0h24v24H0z" fill="none"/></svg>
-            </button>
-          </form>
-        </li>
       </ul>
     </nav>
   </header>