Revert "set content container height to 100 percent"

This commit caused the browser vertical scrollbar to always be active, which in
places like gradebook2 could create a double scrollbar situation.

fixes CNVS-13668

This reverts commit bb454843879604c6c990102cb88595fcb091a865.

test plan:
- go to gradebook2 with enough students to scroll
- you should only have 1 scrollbar

Change-Id: I7e09b539db5752549cc61baacf97500e3ea980cd
Reviewed-on: https://gerrit.instructure.com/36648
Reviewed-by: Drew Bowman <dbowman@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>