Minor: Remove unused Portal.mustache

Should have been removed in
I2549af3e24e5d51c09e9a88ca50a0d9b2e154c3f

Presumably got readded while addressing a rebase conflict

Bug: T249372
Change-Id: Iaff98d8b4770e82277463f39800dd7571e1ed50b

includes/templates/Portal.mustache

@@ -1,23 +0,0 @@
-{{!
-Each portal has the following composition:
-	string portal-id
-	string class of portal
-	string html-tooltip
-	string msg-label-id
-	string? html-userlangattributes
-	string msg-label
-	string html-portal-content
-	string? html-after-portal
-	string? html-hook-vector-after-toolbox is deprecated and used by the toolbox portal.
-}}
-<nav class="{{class}}" id="{{portal-id}}" {{{html-tooltip}}} aria-labelledby="{{msg-label-id}}">
-	<h3 {{{html-userlangattributes}}} id="{{msg-label-id}}">
-		{{msg-label}}
-	</h3>
-	<div class="body">
-		{{{html-portal-content}}}
-		{{{html-after-portal}}}
-	</div>
-</nav>
-{{! Note: html-hook-vector-after-toolbox is deprecated. }}
-{{{html-hook-vector-after-toolbox}}}