remove ie7 hacks from bootstrap mixins
remove ie7 hacks from bootstrap mixins

...since we don't support them anyway

Change-Id: I4f62d3983e2b037139eed94adb488e8561142876
Reviewed-on: https://gerrit.instructure.com/56158
Tested-by: Jenkins
Reviewed-by: Clay Diffrient <9dff2e5c98626d20d2848250c411e8009465bb87@instructure.com>
Product-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>
QA-Review: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>

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