fix custom params not saving.
fix custom params not saving.

fixes PLAT-984

test plan:
add custom setting to an app
try removing all settings
all settings should be removed

Change-Id: I375943e588b52c5ba6ca15e9d06320284ca3fb75
Reviewed-on: https://gerrit.instructure.com/52589
Reviewed-by: Brad Humphrey <9233b6f5388d6867a2a7be14d8b4ba53c86cfde2@instructure.com>
Tested-by: Jenkins
QA-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Product-Review: Brad Humphrey <9233b6f5388d6867a2a7be14d8b4ba53c86cfde2@instructure.com>

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