use sass to remove repetition in flexboxgrid.scss
use sass to remove repetition in flexboxgrid.scss

this just rewrites flexboxgrid.scss to take
advantage of sass's features. it outputs exactly
the same css, just with less lines of source.

Change-Id: Ie201c3bd762c294969e7b25a230cdf23cce7a813
Reviewed-on: https://gerrit.instructure.com/40623
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Chris Hart <b82b40b84a2f06957ec9caf1768340bd6b929cc4@instructure.com>
Product-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
QA-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>

snehakachroo1/LSI_replica,shidao-fm/canvas-lms,venturehive/canvas-lms,djbender/canvas-lms,samuels410/greatlakes-lms,whalejasmine/canvas-lms,instructure/canvas-lms,SwinburneOnline/canvas-lms,dgynn/canvas-lms,snehakachroo1/LSI_replica,SwinburneOnline/canvas-lms,jay3126/canvas-lms,efrj/canvas-lms,kyroskoh/canvas-lms,Jyaasa/canvas-lms,fronteerio/canvas-lms,narigone/canvas,antoniuslin/canvas-lms,venturehive/canvas-lms,ShreniiNepal/shrenii_lmp,HotChalk/canvas-lms,Rvor/canvas-lms,redconfetti/canvas-lms,sdeleon28/canvas-lms,jay3126/canvas-lms,utkarshx/canvas-lms,skmezanul/canvas-lms,shidao-fm/canvas-lms,ShreniiNepal/shrenii_lmp,Jyaasa/canvas-lms,matematikk-mooc/canvas-lms,utkarshx/canvas-lms,va7map/canvas-lms,eCNAP/CANVAS,wrdsb/canvas-lms,shidao-fm/canvas-lms,snehakachroo1/LSI_replica,whalejasmine/canvas-lms,AndranikMarkosyan/lms,fronteerio/canvas-lms,antoniuslin/canvas-lms,shidao-fm/canvas-lms,wye0220/shindig-canvas,wye0220/shindig-canvas,sdeleon28/canvas-lms,utkarshx/canvas-lms,jay3126/canvas-lms,juoni/canvas-lms,ShreniiNepal/shrenii_lmp,venturehive/canvas-lms,skmezanul/canvas-lms,eCNAP/CANVAS,utkarshx/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,roxolan/canvas-lms,matematikk-mooc/canvas-lms,Rvor/canvas-lms,Jyaasa/canvas-lms,juoni/canvas-lms,wrdsb/canvas-lms,grahamb/canvas-lms,kyroskoh/canvas-lms,tgroshon/canvas-lms,redconfetti/canvas-lms,fronteerio/canvas-lms,leftplusrightllc/canvas-lms,AndranikMarkosyan/lms,Rvor/canvas-lms,gbleydon/canvas-lms,juoni/canvas-lms,roxolan/canvas-lms,greyhwndz/canvas-lms,sdeleon28/canvas-lms,HotChalk/canvas-lms,dgynn/canvas-lms,greyhwndz/canvas-lms,va7map/canvas-lms,wrdsb/canvas-lms,va7map/canvas-lms,sfu/canvas-lms,efrj/canvas-lms,Jyaasa/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,narigone/canvas,kyroskoh/canvas-lms,samuels410/greatlakes-lms,gbleydon/canvas-lms,efrj/canvas-lms,leftplusrightllc/canvas-lms,tgroshon/canvas-lms,gbleydon/canvas-lms,sfu/canvas-lms,antoniuslin/canvas-lms,roxolan/canvas-lms,tgroshon/canvas-lms,antoniuslin/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,eCNAP/CANVAS,dgynn/canvas-lms,samuels410/greatlakes-lms,snehakachroo1/LSI_replica,greyhwndz/canvas-lms,grahamb/canvas-lms,skmezanul/canvas-lms,venturehive/canvas-lms,grahamb/canvas-lms,AndranikMarkosyan/lms,tgroshon/canvas-lms,narigone/canvas,leftplusrightllc/canvas-lms,fronteerio/canvas-lms,va7map/canvas-lms,wye0220/shindig-canvas,HotChalk/canvas-lms,grahamb/canvas-lms,redconfetti/canvas-lms,eCNAP/CANVAS,matematikk-mooc/canvas-lms,instructure/canvas-lms,grahamb/canvas-lms,sfu/canvas-lms,whalejasmine/canvas-lms,sdeleon28/canvas-lms,sfu/canvas-lms,jay3126/canvas-lms,greyhwndz/canvas-lms,Rvor/canvas-lms,instructure/canvas-lms,wrdsb/canvas-lms,skmezanul/canvas-lms,HotChalk/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,efrj/canvas-lms,matematikk-mooc/canvas-lms,whalejasmine/canvas-lms,SwinburneOnline/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,AndranikMarkosyan/lms,narigone/canvas,redconfetti/canvas-lms,samuels410/greatlakes-lms,leftplusrightllc/canvas-lms,kyroskoh/canvas-lms,dgynn/canvas-lms,ShreniiNepal/shrenii_lmp