/etc/lighttpd/conf-available/10-no-www.conf is in lighttpd 1.4.33-1+nmu2ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | $HTTP["host"] =~ "^www\.(.*)" {
url.redirect = ( "^/(.*)" => "http://%1/$1" )
}
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