[SE-3949] remove absolute positioning to allow RTL scrolling
This PR fixes RTL scrolling in grade books by removing the absolute positioning of grade-table which prevents scrolling if the direction is not LTR.
*Sandbox URL*: https://se-3949-3.stage.opencraft.hosting/
*Merge deadline*: None
0. Login at https://se-3949-3.stage.opencraft.hosting/login using the standard edx user/password
1. Open the [grade book](https://se-3949-3.stage.opencraft.hosting/courses/course-v1:edX+DemoX+Demo_Course/instructor/api/gradebook)
2. Validate the scrollbar can be scrolled
*Author notes and concerns*:
It is normal and expected if the scrollbar jumps to the right within the grade book after the rules are removed and the language is RTL.
[ ] @pkulkark