noindex comment is visible on some LMS pages

[timmc-edx]

The noindex HTML added in https://github.com/edx/edx-themes/pull/825 includes a template comment, but the comment is showing up on some pages, such as /logout. Apparently this file is sometimes being rendered as a template, and sometimes included as verbatim text.

A/C:

• Stop the text from showing up on pages
  • https://github.com/edx/edx-themes/pull/829
• Find out why it was being displayed verbatim on /logout but not on other pages
• Fix it so that this is always rendered as a template in the future