Remove course nav positioning hack
Remove course nav positioning hack

Chrome has fixed issue 1150774, so this temporary hack to fix scrolling in courses is no longer necessary.

This reverts commit ca69b598a04769a24fef93308d1f1faee2f984fe.

closes LS-1648
flag = none

Test plan:
 - Visit any course page (except discussions, people, outcomes, collaborations, or course settings)
 - Ensure there's enough course content to require scrolling
 - Expect to be able to scroll
 - Expect the course nav to still look OK

Change-Id: I63ac3a41019a5c3c432fec29ade992fa0e945eb3
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/291601
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Robin Kuss <0b206b54367b2de0334896ea45826f0e3194bd35@instructure.com>
QA-Review: Robin Kuss <0b206b54367b2de0334896ea45826f0e3194bd35@instructure.com>
Product-Review: Jackson Howe <318c10a818c1b1f2ec50cdcb1827b2c6c5ebd7dc@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms