That is because you are proxying through Clouflare and Cloudflare always replace the server signature.
As for that particular header, I do not seem to get that header
$ curl -I -H 'User-Agent: Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)' https://www.dragosroua.com/sitemap.xml
HTTP/2 403
date: Sat, 30 Nov 2019 16:55:22 GMT
set-cookie: __cfduid=de1ae694faa8cb306a74de47f4701eca91575132921; expires=Mon, 30-Dec-19 16:55:21 GMT; path=/; domain=.dragosroua.com; HttpOnly
cf-cache-status: DYNAMIC
expect-ct: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
x-turbo-charged-by: LiteSpeed
server: cloudflare
However I get a 403, which appears to be sent by your server.