Reverts inline .scss block to inline .css block

[gdixon]

Description

This PR reverts .scss changes made in commit 4763718.

We made these changes because the css being used in shared_template_head.html is duplicated from the core app's css - in order to DRY up the codebase, we wanted to use a single source of truth, unfortunately django-compressor is failing to inline the .scss block in production.

We will readdress this in the future, the path forward will likely be:

• assess what css is being used by the emails
• refactor and bring just that css into a single new css document and inline that instead of the 3 .css documents we are currently inlining
• rename that new document email_head.css so that there is no ambiguity as to what the file is.

Refers/Fixes

Fixes: 4763718

Testing

Tested locally