unlockDialog: Hide cancel button

As per the latest design review, hide the cancel button
on the unlock dialog.

!1006
6 jobs for !1006 with gbsneto/multi-user-button in 3 minutes and 44 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Review
passed #592392
check_commit_log

00:00:23

passed #592394
eslint

00:00:57

passed #592393
js_check

00:00:29

 
  Build
passed #592395
build

00:01:54

 
  Test
passed #592396
test

00:00:51

passed #592397
test-pot

00:00:50