Fix U2F button icon (#12167)
Fix U2F button icon (#12167)

Previously this used a USB icon which required a separate font file used
nowhere else so replace it with a octicon and fix the background color
on arc-green too.
vCaesar/gitea,sapk-fork/gitea,cez81/gitea,vdbt/gitea,sapk-fork/gitea,go-gitea/gitea,sapk-fork/gitea,sapk-fork/gitea,cez81/gitea,cez81/gitea,go-gitea/gitea,vCaesar/gitea,go-gitea/gitea,vdbt/gitea