Remove 404 not found pontoon.js from staging

[janbrasna]

There is https://pontoon.mozilla.org/pontoon.js referenced in base template.

kitsune/kitsune/sumo/jinja2/base.html

Lines 384 to 387 in fc59b5e

	{# Temporary Pontoon testing - bug 812176 #}
	{% if settings.STAGE %}
	<script src="https://pontoon.mozilla.org/pontoon.js"></script>
	{% endif %}

This is no longer used, and returns 404:

• Drop remnants of in-context localization pontoon#2862
• Remove pontoon.js pontoon#2213