self_enrollment.css was blank in legacy styles
self_enrollment.css was blank in legacy styles

fixes: CNVS-23967

brandable_css has a guard against uploading
completely blank css files to s3
(because usually that would be a bug) but in this
case self_enrollment.css really does do nothing in
legacy UI.

test plan:
* with s3 credentials set up in canvas_cdn.yml:
* run ./node_modules/.bin/brandable_css
* it should not fail

Change-Id: I9ab21c62ce933efe079795a37a3778567223e61e
Reviewed-on: https://gerrit.instructure.com/65058
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Product-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Tested-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>

leftplusrightllc/canvas-lms,venturehive/canvas-lms,venturehive/canvas-lms,fronteerio/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,grahamb/canvas-lms,roxolan/canvas-lms,HotChalk/canvas-lms,roxolan/canvas-lms,redconfetti/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,redconfetti/canvas-lms,grahamb/canvas-lms,HotChalk/canvas-lms,leftplusrightllc/canvas-lms,redconfetti/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms,SwinburneOnline/canvas-lms,SwinburneOnline/canvas-lms,SwinburneOnline/canvas-lms,redconfetti/canvas-lms,fronteerio/canvas-lms,roxolan/canvas-lms,HotChalk/canvas-lms,roxolan/canvas-lms,grahamb/canvas-lms,leftplusrightllc/canvas-lms,fronteerio/canvas-lms,djbender/canvas-lms,venturehive/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,fronteerio/canvas-lms,leftplusrightllc/canvas-lms,djbender/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms