Switch ConfirmDialog from using strings to using l10nIds.

https://bugzilla.mozilla.org/show_bug.cgi?id=1041404
Oh yeah, I am changing that to epllipsis charachter. Earlier I just copied and pasted from https://github.com/mozilla-b2g/gaia/pull/23278/files#diff-5103fd344bb675ceaf85e469d6f3022bL103

What should I change the key to? How about `connectingEllipsis`?