Second try at removing LTI padding
Second try at removing LTI padding

closes INTEROP-7290
refs INTEROP-7095

Test plan:
- choose a few placements to look at. I looked at an LTI-type assignment
  and global/account nav. Maybe you can think of some others.
- before checking out this commit observe the width and height of the
  iframe at varying widths. For small widths, use the "Device Mode" of
  your browser's (Chrome/Firefox) dev tools.
- check out commit and compile assets with "yarn build:css" if necessary
- view your placements and again use dev tools' responisve design mode
  to control the width of the screen. On each placement:
  - make sure the height of the iframe is not different from before this
    change.
  - notice that at a width of 368px the padding disappears. (Make sure
    your zoom level is 100%)
  - select the iframe and check the "computed" tab. check that the tool is
    given at least 320px of width when the screen is 320px, 368px, and
    369px wide.
  - make sure the content is not clipped on the sides (they had this
    problem in Wiki Pages when they tried to set the negative margin
    directly on the iframe, but it doesn't seem to be a problem in these
    placements)

Change-Id: I63463f8a4dd1f9c50c5672fafbd9e204cc43bb80
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/285347
Product-Review: Evan Battaglia <e557ffdfc4b80aab44858030b0ae5370b86cb7b1@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>
QA-Review: Xander Moffatt <27f70fe194da423604e6e0a63a3de19814736fa9@instructure.com>

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