We have some Sass files that basically generate duplicates of other
Sass files and are no longer referenced from any pages. This looks
like it might have been stuff that never got cleaned up when
comprehensive themeing was done.

List of removed files and what they were replaced by:

    application.scss ->  lms-main.scss
    application-rtl.scss -> lms-main-rtl.scss
    course.scss -> lms-course.scss
    course-rtl.scss -> lms-course-rtl.scss

This should help speed up the Sass compile.