Accessibility: Labeled remove external feed link
Accessibility: Labeled remove external feed link

Fixes CNVS-13902

Test plan:
- Visit the announcements page.
- Add an external feed
- Using a screen reader, insure that the remove feed link has a meaningful
  label.

Change-Id: I54797e9d150e16e3edaad0a9869aeb1d7ffdf254
Reviewed-on: https://gerrit.instructure.com/37830
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Jayce Higgins <8f0644d105785a923e938c7b131e3ab930cb6139@instructure.com>
Product-Review: Matthew Wheeler <ce71fbafda91d6c8f12582e1837687d5fe592dd9@instructure.com>
QA-Review: David Josse <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@instructure.com>
Tested-by: David Josse <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@instructure.com>

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