luci-app-https-dns-proxy: remove redundant cbi-value-field div

The redundant "cbi-value-field" div introduces uneeded margin, remove this
element to fix the view layout.

Suggested-by: Santiago Kozak <arbolitoloco1@protonmail.com>
[reword commit message]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>