[FIX] mass_mailing: remove duplicated JS file import

If a user wants to unsubscribe from a mass mailing, he will get a traceback
when doing so. This is due to a file being imported twice. Indeed unsubscribe
file is imported in mass_mailing.layout that calls assets_backend that already
imports unsubscribe.

It seems there is no traceback in 13 but well in 13.2. However we can clean it
in 13. It has been introduced at f296992317 .

Task-2241443

closes odoo/odoo#50722

X-original-commit: 521eb273ce792eb99631fe34faf7d512e3b59a8e
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/mass_mailing/views/mass_mailing_templates_portal.xml

@@ -115,7 +115,6 @@
             <t t-set="head">
                 <t t-call-assets="web.assets_common"/>
                 <t t-call-assets="mass_mailing.assets_backend"/>
-                <script type="text/javascript" src="/mass_mailing/static/src/js/unsubscribe.js"></script>
             </t>
             <body class="o_white_body">
                 <header>